Liquid crystal display device, semiconductor device, and electronic appliance

ABSTRACT

The liquid crystal display device includes an island-shaped first semiconductor film  102  which is formed over a base insulating film  101  and in which a source  102   d , a channel forming region  102   a , and a drain  102   b  are formed; a first electrode  102   c  which is formed of a material same as the first semiconductor film  102  to be the source  102   d  or the drain  102   b  and formed over the base insulating film  101 ; a second electrode  108  which is formed over the first electrode  102   c  and includes a first opening pattern  112 ; and a liquid crystal  110  which is provided over the second electrode  108.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/695,898, filed Apr. 3, 2007, now pending, which claims the benefit ofa foreign priority application filed in Japan as Serial No. 2006-105618on Apr. 6, 2006, both of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, a liquidcrystal display device, and an electronic appliance including them. Inparticular, the present invention relates to a semiconductor device anda liquid crystal display device in which an electric field generallyparallel to a substrate is generated to control liquid crystalmolecules, and an electronic appliance including the semiconductordevice or the liquid crystal display device.

2. Description of the Related Art

As one of plans for technical development of a liquid crystal displaydevice, to widen a viewing angle can be given. As a technique forrealizing a wide viewing angle, a mode in which an electric fieldgenerally parallel to a substrate is generated and liquid crystalmolecules are moved in a plane parallel to the substrate to controlgrayscale is employed. As such a mode, IPS (In-Plane Switching) and FFS(Fringe-Field Switching) are given. In these modes, a first electrode(such as a pixel electrode with which voltage is controlled for eachpixel) having a slit (an opening pattern) is located under a liquidcrystal and a second electrode (such as a common electrode with whichcommon voltage is applied to all pixels) is located under the firstelectrode. An electric field is applied between the pixel electrode andthe common electrode, so that the liquid crystal is controlled. Withsuch layout, an electric field in a direction parallel to a substrate isapplied to the liquid crystal. Therefore, the liquid crystal moleculescan be controlled with the electric field. That is, the liquid crystalmolecules which are aligned parallel to the substrate (so calledhomogeneous alignment) can be controlled in a direction parallel to thesubstrate; therefore, viewing angle is increased.

Conventionally, both common electrode and pixel electrode are formed ofITO (indium tin oxide) (Patent Document 1: Japanese Published PatentApplication No. 2000-89255 (FIG. 5 and 14th paragraph)).

SUMMARY OF THE INVENTION

As described above, in the case of employing a structure in which thesecond electrode (such as the common electrode) is located under thefirst electrode (such as the pixel electrode), both the common electrodeand the pixel electrode are formed of ITO conventionally. Accordingly,the numbers of manufacturing steps and masks, and manufacturing costhave been increased. The present invention is made in view of theforegoing, and an object of the present invention is to provide a liquidcrystal display device and an electronic appliance with wide viewingangle, having less numbers of manufacturing steps and masks and lowmanufacturing cost compared with a conventional device; and to provide amanufacturing method of the liquid crystal display device.

To solve the aforementioned problems, a liquid crystal display deviceaccording to the present invention includes a first electrode formedover a substrate, an insulating film formed over the first electrode, asecond electrode formed over the insulating film, and a liquid crystalprovided over the second electrode; in which the second electrode has anopening pattern and the first electrode has a semiconductor filmcontaining silicon.

A semiconductor device according to the present invention includes afirst electrode formed over a substrate, an insulating film formed overthe first electrode, and a second electrode formed over the insulatingfilm; in which the second electrode has an opening pattern and the firstelectrode has a semiconductor film containing silicon

A liquid crystal display device according to the present inventionincludes a first electrode formed over a substrate, an insulating filmformed over the first electrode, a second electrode formed over theinsulating film, a liquid crystal provided over the second electrode,and a transistor formed over the substrate; in which the secondelectrode has an opening pattern, the first electrode has asemiconductor film containing silicon, the transistor has asemiconductor film containing silicon, and the semiconductor filmincluded in the first electrode is formed at the same time as thesemiconductor film included in the transistor.

A semiconductor device according to the present invention includes afirst electrode formed over a substrate, an insulating film formed overthe first electrode, a second electrode formed over the insulating film,and a transistor formed over the substrate; in which the secondelectrode has an opening pattern, the first electrode has asemiconductor film containing silicon, the transistor has asemiconductor film containing silicon, and the semiconductor filmincluded in the first electrode is formed at the same time as thesemiconductor film included in the transistor.

In the liquid crystal display device and the semiconductor device, thefirst electrode and the semiconductor film included in the transistorare formed at the same time, and then, etched and patterned at the sametime. Accordingly, the first electrode and the semiconductor filmincluded in the transistor contain the same material. In addition, ann-type impurity or a p-type impurity is introduced thereto at the sametime in some cases. In such a case, they have a portion withapproximately the same concentration of the impurity. Note that thetransistor includes a portion to which the impurity is introduced, aportion to which the impurity is slightly introduced, a portion to whichthe impurity is hardly introduced, and the like. The first electrode isgenerally in the same states as the portion in the semiconductor filmincluded in the transistor, to which the impurity is introduced in manycases. Thus, the first electrode can be formed at the same time as thetransistor. Therefore, an additional step is not required to form thefirst electrode. In addition, a liquid crystal display device with wideviewing angle and low manufacturing cost compared with a conventionaldevice can be provided.

Note that the opening pattern includes not only a closed opening patternsuch as a slit, but also a space which is located between the conductivepatterns and in which the conductive pattern is not formed, such as aspace between the comb-teeth of a comb-shaped electrode. The same can beapplied to description hereinafter.

Note that in the aforementioned liquid crystal display device and thesemiconductor device, a portion in which first and second interlayerinsulating films are provided between the first electrode and the secondelectrode, and the second electrode and the first electrode except forthe opening pattern are overlapped each other the first electrode; thefirst interlayer insulating film, and the second electrode can functionas a capacitor. In this case, storage capacitance can be increased.Therefore, when a thin film transistor is turned off, the potential ofthe pixel electrode can be easily kept.

A liquid crystal display device according to the present inventionincludes a first electrode formed over a substrate, an insulating filmformed over the first electrode, a second electrode formed over theinsulating film, a liquid crystal provided over the second electrode,and a transistor formed over the substrate; in which the secondelectrode includes an opening pattern, the first electrode includes asemiconductor film containing silicon, the semiconductor film includedin the first electrode is formed at the same time as the semiconductorfilm included in the transistor, and the semiconductor film included inthe first electrode and the semiconductor film included in thetransistor contain an impurity having the same conductivity type.

A semiconductor device according to the present invention includes afirst electrode formed over a substrate, an insulating film formed overthe first electrode, a second electrode formed over the insulating film,and a transistor formed over the substrate; in which the secondelectrode includes opening pattern, the first electrode includes asemiconductor film containing silicon, the semiconductor film includedin the first electrode is formed at the same time as the semiconductorfilm included in the transistor, and the semiconductor film included inthe first electrode and the semiconductor film included in thetransistor contain an impurity having the same conductivity type.

When the first electrode and the transistor contain the impurity havingthe same conductivity type (such as an n-type or a p-type), the layoutcan be efficient. Accordingly, the aperture ratio can be improved.

A liquid crystal display device according to the present inventionincludes a transistor formed over a substrate, a semiconductor filmformed in the transistor, a first electrode formed by a part of thesemiconductor film, an insulating film formed over the first electrode,a second electrode formed over the insulating film, and a liquid crystalprovided over the second electrode; in which the second electrodeincludes an opening pattern.

A semiconductor device according to the present invention includes atransistor formed over a substrate, a semiconductor film formed in thetransistor, a first electrode formed by a part of the semiconductorfilm, an insulating film formed over the first electrode, and a secondelectrode formed over the insulating film; in which the second electrodeincludes an opening pattern.

When the first electrode and the semiconductor film included in thetransistor are formed in one island as described above, the layout canbe efficient. Accordingly, the aperture ratio can be improved.

In the aforementioned structure of the liquid crystal display deviceaccording to the present invention, the first electrode is a pixelelectrode and the second electrode is a common electrode.

In the aforementioned structure of the semiconductor device according tothe present invention, the first electrode is a pixel electrode and thesecond electrode is a common electrode.

In the aforementioned structure of the liquid crystal display deviceaccording to the present invention, the first electrode is a commonelectrode and the second electrode is a pixel electrode.

In the aforementioned structure of the semiconductor device according tothe present invention, the first electrode is a common electrode and thesecond electrode is a pixel electrode.

In the aforementioned structure of the liquid crystal display deviceaccording to the present invention, orientation of the liquid crystal iscontrolled by an electric field between the first electrode and thesecond electrode.

Note that a switch shown in the present invention may be any switch suchas an electrical switch or a mechanical switch. That is, as long ascurrent flow can be controlled, any type of switch can be used withoutbeing limited to a particular type. For example, a transistor, a diode(such as a PN diode, a PIN diode, a Schottky diode, or a diode-connectedtransistor), or a logic circuit that is a combination thereof may beused. In the case of using a transistor as a switch, a polarity(conductivity) type of the transistor is not particularly limitedbecause it operates as a mere switch. However, when off current ispreferred to be small, a transistor of a polarity with smaller offcurrent is desirably used. As a transistor with small off current, atransistor having an LDD region, a transistor having a multigatestructure, and the like are given. Further, an N channel transistor isdesirably used when a potential of a source terminal of the transistorfunctioning as a switch is close to a low potential side power source(Vss, GND, 0V, or the like). On the other hand, a P-channel transistoris desirably used when the potential of the source terminal is close toa high potential side power source (Vdd or the like). This is because itis easy for a transistor to function as a switch when an absolute valueof a gate-source voltage is increased. Note that a CMOS switch can alsobe applied by using both N-channel and P-channel transistors. With aCMOS switch, an operation can be appropriately performed even when thesituation changes such that a voltage outputted through the switch (thatis, an input voltage) is higher or lower than an output voltage.Although as a switch in the present invention, a TFT controlling a pixelelectrode, a switch element used in a driver circuit portion, and thelike are given; a switch can be employed in another part, if currentflow is required to be controlled.

In the present invention, “being connected” includes “being electricallyconnected” and “being directly connected”. Here, “being electricallyconnected” refers to a state in which an element capable of electricconnection (such as a switch, a transistor, a capacitor, an inductor aresistor, or a diode) may be interposed in the predetermined connection.In addition, “being directly connected” refers to only a specific caseof “being electrically connected”, where no element capable of electricconnection is interposed and direct connection is achieved. That is,“being directly connected” specifically refers to “being electricallyconnected” without another element interposed in the predeterminedconnection. Note that the description “being directly connected” meansthe same as “being connected in a direct manner” is also used.

Note that a display element, a display device, and a light emittingdevice can employ various modes or can include various elements. Forexample, a display medium whose contrast varies by an electromagneticaction can be used, such as an EL element (an organic EL element, aninorganic EL element, or an EL element including organic and inorganicsubstances), an electron emitting element, a liquid crystal element,electron ink, a grating light valve (GLV), a plasma display panel (PDP),a digital micromirror device (DMD), a piezoceramic display, or a carbonnanotube. Note that a display device using an EL element includes an ELdisplay; a display device using an electron emitting element includes afield emission display (FED), an SED flat panel display (SED:Surface-conduction Electron-emitter Display), and the like; a displaydevice using a liquid crystal element includes a liquid crystal display,a transmissive liquid crystal display, a transflective liquid crystaldisplay, and a reflective liquid crystal display; and a display deviceusing electronic ink includes electronic paper. As an application of thepresent invention other than a liquid crystal element, for example, anelectrode containing silicon is used for an electrode in an EL elementand the like. Therefore, an element such as an EL element can bemanufactured at low cost. In this case, an electrode may have an openingpattern, but not necessarily. When an electrode containing silicon ofthe present invention is used in an organic EL element, a structure inwhich a layer containing an organic compound is interposed betweenelectrodes is favorably employed, but not necessarily. On the otherhand, when the electrode containing silicon of the present invention isused in an inorganic EL element, a structure in which a layer containingan inorganic compound is interposed between electrodes may be employed,or a structure in which a layer containing an inorganic compound isformed over the electrode may be employed; since AC drive is possible inthe inorganic EL element. In the latter structure, light emission can becarried out with use of a lateral electric field formed by a firstelectrode and a second electrode. With such a structure, a componentwhich attenuates light from the electrode or the like is not necessarilyprovided on a light emitting side, accordingly, luminance of the ELdisplay device is improved and deterioration of the EL display device issuppressed.

Note that various types of transistors can be applied to the presentinvention and an applicable type of the transistor is not limited.Accordingly, the present invention can employ a thin film transistor(TFT) using a non-single crystalline semiconductor film typified byamorphous silicon or polycrystalline silicon, a transistor using asemiconductor substrate or an SOI substrate, a MOS transistor, ajunction transistor, a bipolar transistor, a transistor using a compoundsemiconductor such as ZnO or a-InGaZnO, a transistor using an organicsemiconductor or a carbon nanotube, and the like. In addition, a type ofsubstrate on which a transistor is provided is not particularly limited.The transistor can be formed on a single crystalline substrate, an SOIsubstrate, a glass substrate, a plastic substrate, a paper substrate, acellophane substrate, a stone substrate, or the like. In addition, afterforming a transistor over a substrate, the transistors may be transposedto another substrate to be located thereon.

Note that as described above, in the present invention, various types oftransistor can be used and can be formed over any substrate. Therefore,all circuits may be formed over a glass substrate, a plastic substrate,a single crystalline substrate, an SOI circuit, or any other circuit.When all circuits are formed on one substrate, the cost can be reducedby reducing the number of components and the reliability can be improvedby reducing the number of connection to components in the circuits.Alternatively, it is possible that some circuits are formed on asubstrate and some other circuits are formed on another substrate. Thatis, all of the circuits are not necessarily formed over one substrate.For example, some circuits are formed over a glass substrate with a useof a transistor while some other circuits are formed over a singlecrystalline substrate, and the IC chip may be connected to the glasssubstrate by COG (Chip On Glass) to be located thereover. Alternatively,the IC chip may be connected to the glass substrate by TAB (Tape AutoBonding) or by using a printed board. In this manner, when some circuitsare formed over one substrate, the cost can be reduced by reducing thenumber of components and the reliability can be improved by reducing thenumber of connection to components in the circuits. Further, whenportions with high drive voltage or high drive frequency, which consumemore power, are not formed on one substrate, increase in powerconsumption can be prevented.

It is to be noted that a transistor can have various structures andmodes, and is not limited to a specific structure. For example, amultigate structure which has two or more gates may be employed as well.With a multigate structure, off current can be reduced and reliabilitycan be improved by improving the pressure resistance of a transistor,and flat characteristics can be obtained such that a drain-sourcecurrent hardly changes even when a drain-source voltage changes inoperation in a saturation region. Alternatively, a structure in whichgate electrodes may be provided over and under a channel may beemployed. With such a structure in which gate electrodes are providedover and under a channel, a current value can be easily increased sincea channel forming region increases, an S value (sub-thresholdcoefficient) can be reduced since a depletion layer is easily formed.Further alternatively, a structure in which a gate electrode is providedover a channel or under the channel may be employed. Also, a forwardstaggered structure or an inversed staggered structure may be employed.A channel forming region may be divided into a plurality of regions,connected in parallel, or connected in series. Further, a sourceelectrode or a drain electrode may overlap with a channel (or a partthereof). Accordingly, with such a structure in which a source electrodeor a drain electrode overlaps with a channel (or a part of thereof),charges are accumulated in a part of the channel and an unstableoperation can be prevented. Further, an LDD region may be provided. Byproviding an LDD region, off current can be reduced and reliability canbe improved by improving the withstand voltage of a transistor, and flatcharacteristics can be obtained such that a drain-source current hardlychanges even when a drain-source voltage changes in operation in asaturation region.

Note that in the present invention, one pixel corresponds to one elementwhich can control brightness. Therefore, for example, one pixel showsone color element by which brightness is expressed. Accordingly, in thecase of a color display device formed of color elements of R (red), G(green), and B (blue), the smallest unit of an image includes threepixels of an R pixel, a G pixel, and a B pixel. Note that color elementsare not limited to three colors and may be more colors, and RGBW (W iswhite) or RGB to which another color such as yellow, cyan, or magenta isintroduced may be used, for example. Further, when one color element iscontrolled by using a plurality of regions, one of the regionscorresponds to one pixel. For example, in the case of performing an areagray scale display, a plurality of regions are provided for one colorelement to control the brightness, which express gray scale as a whole.One of the regions to control the brightness corresponds to one pixel.Therefore, in that case, one color element includes a plurality ofpixels. In that case, a region which contributes to display an image maydiffer in size depending on the pixels. Further, in a plurality ofregions controlling the brightness which are provided for one colorelement, that is, in a plurality of pixels included in one colorelement, signals provided to each pixel may slightly differ from oneanother so that the viewing angle is expanded. Note that the description“one pixel (for three colors)” corresponds to three pixels of R, G, andB which are considered as one pixel; while “one pixel (for one color)”corresponds to a plurality of pixels provided for one color elementwhich are collectively considered as one pixel.

Note that in the present invention, there is a case where pixels arearranged in matrix. The case where pixels are arranged in matrixincludes not only to a case where the pixels are arranged in a stripepattern, which is a so-called grid configuration where longitudinalstripes and lateral stripes cross each other, but also to a case wherethree color elements are arranged in a so-called delta pattern when afull color display is performed using three color elements (for example,RGB). Further, a Bayer arrangement is also included. Note that the colorelement is not limited to three colors and may have more colors, forexample, RGBW (W is white) or RGB to which yellow, cyan, or magenta isadded. The size of a light emission area may be different depending oncolor elements.

A transistor is an element including at least three terminals of a gate,a drain, and a source. A channel forming region is provided between adrain region and a source region. Here, it is difficult to determinewhich of two terminals is a source or a drain since it depends on astructure, operating condition, and the like of the transistor.Therefore, in the present invention, regions which function as a sourceand a drain are referred to as a first terminal and a second terminal,respectively.

Note that a gate includes a gate electrode and a gate wiring (alsoreferred to as a gate line, a gate signal line, or the like) or a partthereof. A gate electrode corresponds to a conductive film a part ofwhich overlaps with a semiconductor forming a channel forming region, anLDD (Lightly Doped Drain) region, or the like, with a gate insulatingfilm interposed therebetween. A gate wiring corresponds to a wiring forconnecting gate electrodes of each pixel and a wiring for connecting agate electrode and another wiring.

However, there is a part which functions as a gate electrode and also asa gate wiring. Such a region may be referred to as a gate electrode or agate wiring. That is, there is a region which cannot be distinguished asa gate electrode or a gate wiring. For example, in a case where achannel forming region overlaps with a gate wiring which is extended,the overlapped region functions both as a gate wiring and as a gateelectrode. Therefore, such a region may be referred to as a gateelectrode or a gate wiring.

Further, a region which is formed of the same material as a gateelectrode and connected to the gate electrode may be referred to as agate electrode as well. Similarly, a region which is formed of the samematerial as a gate wiring and connected to the gate wiring may bereferred to as a gate wiring. In a strict sense, such a region does notoverlap with a channel forming region or does not have a function toconnect to another gate electrode in some cases. However, there is aregion which is formed of the same material as a gate electrode or agate wiring and connected to the gate electrode or the gate wiring dueto manufacturing cost, reduction of steps, layout, and the like.Therefore, such a region may also be referred to as a gate electrode ora gate wiring.

For example, in a multigate transistor, gate electrodes of onetransistor and another transistor are often connected through aconductive film formed of the same material as the gate electrode. Sucha region for connecting the gate electrodes may be referred to as a gatewiring, or may be referred to as a gate electrode when a multigatetransistor is considered as one transistor. That is, a component whichis formed of the same material as a gate electrode or a gate wiring andconnected to the gate electrode or the gate wiring may be referred to asa gate electrode or a gate wiring. Moreover, for example, a portion of aconductive film which connects a gate electrode and a gate wiring mayalso be referred to as a gate electrode or a gate wiring.

Note that a gate terminal corresponds to a part of a region of a gateelectrode or a region electrically connected to the gate electrode.

Note that a source includes a source region, a source electrode, and asource wiring (also referred to as a source line, a source signal line,or the like) or a part thereof. A source region corresponds to asemiconductor region which contains a large amount of p-type impurities(boron, gallium, or the like) or n-type impurities (phosphorus, arsenic,or the like). Therefore, a region containing a small amount of p-typeimpurities or n-type impurities, that is, an LDD (Lightly Doped Drain)region is not included in a source region. A source electrodecorresponds to a conductive layer a part of which is formed of adifferent material from a source region and electrically connected tothe source region. Note that a source electrode including a sourceregion is sometimes referred to as a source electrode. A source wiringcorresponds to a wiring for connecting source electrodes of each pixeland a wiring for connecting a source electrode and another wiring.

However, there is a part which functions as a source electrode and alsoas a source wiring. Such a region may be referred to as a sourceelectrode or a source wiring. That is, there is a region which cannot bedistinguished as a source electrode or a source wiring. For example,when there is a source region overlapping with a source wiring which isextended, the region functions as a source wiring and also as a sourceelectrode. Therefore, such a region may be referred to as a sourceelectrode or a source wiring.

Further, a region which is formed of the same material as a sourceelectrode and connected to the source electrode; or a part whichconnects one source electrode and another source electrode may also bereferred to as a source electrode. Further, a part overlapping with asource region may be referred to as a source electrode. Similarly, aregion which is formed of the same material as a source wiring andconnected to the source wiring may be referred to as a source wiring. Ina strict sense, there is a case where such a region does not have afunction to connect one source electrode to another source electrode.However, there is a region which is formed of the same material as asource electrode or a source wiring and connected to the sourceelectrode or the source wiring due to manufacturing cost, reduction ofsteps, layout, and the like. Therefore, such a region may also bereferred to as a source electrode or a source wiring.

For example, a conductive film a part of which connects a sourceelectrode and a source wiring may be referred to as a source electrodeor a source wiring.

Note that a source terminal corresponds to a part of a source region, asource electrode, or a region electrically connected to a sourceelectrode.

Note that a drain is similar to a source.

Note that in the present invention, a semiconductor device correspondsto a device including a circuit having a semiconductor element (atransistor, a diode, or the like). Further, a semiconductor device maycorrespond to a general device which functions by utilizingsemiconductor characteristics. A display device corresponds to a deviceincluding a display element (a liquid crystal element, a light emittingelement, or the like). Note that a display device may correspond to adisplay panel itself in which a plurality of pixels including displayelements such as a liquid crystal element or an EL element and aperipheral driver circuit for driving the pixels are formed over asubstrate. Moreover, a display device may include a device provided witha flexible printed circuit (FPC) or a printed wiring board (PWB).Further, a light emitting device corresponds to a display deviceincluding a self-luminous light emitting element such as an EL elementor an element used for an FED, in particular. A liquid crystal displaydevice corresponds to a display device including a liquid crystalelement.

In the present invention, an expression that an object is formed on orformed over a different object does not necessarily mean that the objectis in direct contact with the different object. The expression mayinclude a case where two objects are not in direct contact with eachother, that is, a case where another object is interposed therebetween.Accordingly, for example, when it is described that a layer B is formedon (or over) a layer A, it means either case where the layer B is formedon and in direct contact with the layer A, or where another layer (forexample, a layer C or a layer D) is formed on and in direct contact withthe layer A and the layer B is formed on and in direct contact with thelayer C or D. Similarly, when it is described that an object is formedabove a different object, it does not necessarily mean that the objectis in direct contact with the different object, and another object maybe interposed therebetween. Accordingly, for example, when it isdescribed that a layer B is formed above a layer A, it means either casewhere the layer B is formed in direct contact with the layer A, or whereanother layer (for example, a layer C or a layer D) is formed in directcontact with the layer A and the layer B is formed in direct contactwith the layer C or D. Similarly, when it is described that an object isformed below or formed under a different object, it means either casewhere the objects are in direct contact with each other or not incontact with each other. In addition, if not specifically limited, onesurface of a substrate is referred to as an upper direction, and theother surface of the substrate is referred to as a lower direction. Thatis, in a case where a layer B is formed over a layer A in manufacturingsteps, its structure can be considered as a structure where the layer Bis formed over the layer A, even when a completed product is turnedupside down. That is, an expression over or under only refers to a sideof an object to which another object is formed, and does not have ageneral meaning of over or under, which is “a direction with respect togravity”. Needless to say, similar description can be applied to otherdirections such as left or light. Note that it is not limited theretowhen it is particularly specified, and the direction of gravity or thelike may be employed as a standard.

With the present invention, a semiconductor film in a transistor and afirst electrode for driving a liquid crystal can be formed in the samestep. As a result, the first electrode can be manufactured withoutincreasing the numbers of masks (reticles) and manufacturing steps.

Accordingly, a liquid crystal display device with wide viewing angle andlow manufacturing cost compared with a conventional device can beprovided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a plan view for illustrating a structure of a liquid crystaldisplay device according to the present invention, and FIG. 1B is across-sectional view along a line A-B of FIG. 1A;

FIG. 2A is a plan view for illustrating a structure of a liquid crystaldisplay device according to the present invention, and FIG. 2B is across-sectional view along a line A-B of FIG. 2A;

FIG. 3A is a plan view for illustrating a structure of a liquid crystaldisplay device according to the present invention, and FIG. 3B is across-sectional view along a line A-B of FIG. 3A;

FIG. 4A is a plan view for illustrating a structure of a liquid crystaldisplay device according to the present invention, and FIG. 4B is across-sectional view along a line A-B of FIG. 4A;

FIG. 5A is a plan view for illustrating a structure of a liquid crystaldisplay device according to the present invention, and FIG. 5B is across-sectional view along a line A-B of FIG. 5A;

FIG. 6A is a plan view for illustrating a structure of a liquid crystaldisplay device according to the present invention, and FIG. 6B is across-sectional view along a line A-B of FIG. 6A;

FIG. 7A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 1, and FIG. 7B is across-sectional view along lines A-B and C-D of FIG. 7A;

FIG. 8 illustrates another structure of FIG. 7B;

FIG. 9A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 2, and FIG. 9B is across-sectional view along lines A-B and C-D of FIG. 9A;

FIG. 10A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 3, and FIG. 10B is across-sectional view along lines A-B, C-D, and E-F of FIG. 10A;

FIG. 11A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 4, and FIG. 11B is across-sectional view along lines A-B and C-D of FIG. 11A;

FIG. 12A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 5, and FIG. 12B is across-sectional view along lines A-B and C-D of FIG. 12A;

FIG. 13A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 6, and FIG. 13B is across-sectional view along lines A-B,C-D, and E-F of FIG. 13A;

FIG. 14A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 7, and FIG. 14B is across-sectional view along lines A-B,C-D, and E-F of FIG. 14A;

FIG. 15A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 8, and FIG. 15B is across-sectional view along lines A-B,C-D, and E-F of FIG. 15A;

FIG. 16A is a circuit diagram of a liquid crystal display deviceaccording to Embodiment Mode 9 and FIG. 16B is a circuit diagram of aliquid crystal display device according to Embodiment Mode 10;

FIG. 17A is a circuit diagram of a liquid crystal display deviceaccording to Embodiment Mode 11 and FIG. 17B is a circuit diagram of aliquid crystal display device according to Embodiment Mode 12;

FIG. 18A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 13, and FIG. 18B is across-sectional view along lines A-B and C-D of FIG. 18A;

FIG. 19A is a cross-sectional view for illustrating a structure of aliquid crystal display device according to Embodiment Mode 14, and FIG.19B is a cross-sectional view for illustrating a structure of a liquidcrystal display device according to Embodiment Mode 15;

FIG. 20 is a cross-sectional view for illustrating a structure of aliquid crystal display device according to Embodiment Mode 16;

FIG. 21A is a plan view of a liquid crystal display device shown in FIG.20 and FIG. 21B is an enlarged view of a pixel portion of FIG. 21A;

FIG. 22A is a plan view of a liquid crystal display device according toEmbodiment Mode 17 and FIG. 22B is an enlarged view of a pixel portionof FIG. 22A;

FIG. 23 is a cross-sectional view for illustrating a structure of aliquid crystal display device according to Embodiment Mode 18;

FIGS. 24A to 24D are plan views for illustrating shapes of an electrodeof an FFS mode liquid crystal display device according to EmbodimentMode 19;

FIGS. 25A to 25D are plan views for illustrating shapes of an electrodeof an IPS mode liquid crystal display device according to EmbodimentMode 20;

FIGS. 26A to 26E are cross-sectional views illustrating a manufacturingmethod of a liquid crystal display module of Embodiment 1;

FIGS. 27A to 27D are cross-sectional views illustrating a manufacturingmethod of a liquid crystal display module of Embodiment 1;

FIG. 28A is a plan view of a liquid crystal display module of Embodiment1 and FIG. 28B is a cross-sectional view along a line K-L of FIG. 28A;

FIGS. 29A and 29B are diagrams for illustrating a liquid crystal displaymodule according to Embodiment 2;

FIGS. 30A and 30B are diagrams for illustrating a liquid crystal displaymodule according to Embodiment 2;

FIGS. 31A to 31H are perspective views illustrating electronicappliances of Embodiment 3;

FIGS. 32A and 32B are cross-sectional views for illustrating a structureof an inorganic EL element according to Embodiment Mode 21;

FIG. 33 is a cross-sectional view for illustrating a structure of anorganic EL element according to Embodiment Mode 22; and

FIGS. 34A to 34D are cross-sectional views for illustrating a structureand manufacturing steps of a reflective liquid crystal display deviceaccording to Embodiment Mode 23.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiment modes and embodiments in the present inventionare described with reference to the accompanying drawings. However, thepresent invention can be carried out with many different modes and it iseasily understood by those skilled in the art that modes and details canbe modified in various ways without departing from the purpose and thescope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the description of theembodiment modes and embodiments.

Embodiment Mode 1

FIGS. 1A and 1B illustrate a basic example of the present invention.FIG. 1A is a plan view and FIG. 1B is a cross-sectional view.

A first electrode 102 is formed over a substrate 100. The firstelectrode 102 is formed with use of ITO (indium tin oxide)conventionally.

In the present invention, the first electrode 102 is formed of, forexample, a semiconductor material containing silicon, although notlimited thereto. Alternatively, amorphous silicon may be used but inorder to enhance conductivity, polysilicon (polycrystalline silicon),single crystalline silicon, and the like may be used. Further, in manycases, the first electrode contains an impurity (a p-type impurity or ann-type impurity) such as phosphorus, boron, gallium, or arsenic tofurther enhance the conductivity.

The reason of using a semiconductor material containing silicon for thefirst electrode 102 is that silicon has high transmittance. In addition,since the first electrode 102 is thin, it can transmit light. Thetransmittance is preferably 50% or more, more preferably, 80% or more,so that higher visibility can be achieved.

Note that an insulating layer or a conductive layer may be providedbetween the substrate 100 and the first electrode 102. For example, aninsulating layer for blocking an impurity intruding from the substrate100, a gate electrode, a gate wiring, a gate insulating film, and thelike may be provided.

An insulating film 106 is formed over the first electrode 102. Note thatthe insulating film 106 may have a single-layer structure or astacked-layer structure.

An inorganic material or an organic material can be used for theinsulating film 106. As an organic material, polyimide, acrylic,polyimide, polyimide amide, resist, siloxane, polysilazane, or the likecan be used. As an inorganic material, an insulating substancecontaining oxygen or nitrogen, such as silicon oxide (SiO_(x)), siliconnitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y): x>y), or siliconnitride oxide (SiN_(x)O_(y): x>y) can be used. Alternatively, astacked-layer film in which a plurality of these films are stacked maybe used. Further alternatively, a stacked-layer film in which an organicmaterial and an inorganic material are combined may be used.

Note that when an inorganic material is used for the insulating film,intrusion of moisture or an impurity can be prevented. In particular, alayer containing nitrogen can block moisture or an impurity efficiently.

Note that when an organic material is used for the insulating film, asurface thereof can be planarized. Accordingly, the insulating film canhave a good effect on a layer provided thereover. For example, the layerformed over the organic material can be planarized, so that disturbanceof orientation of the liquid crystal can be prevented, cutting of awiring can be prevented, and a resist can be formed with accuracy.

A second electrode 108 is formed overt the insulating film 106. Thesecond electrode 108 may be formed of a material with a highlight-transmitting property. For example, one or more elements selectedfrom indium (In), tin (Sn), and oxygen (O); or a compound or an alloymaterial containing one or more of the aforementioned elements as acomponent (such as indium tin oxide (ITO), indium zinc oxide (IZO), orindium tin oxide doped with silicon oxide (ITSO)) are desirable. Inparticular, IZO is preferable since it is easy to be patterned andformed into a minute shape with accuracy, although it is not limitedthereto.

Note that the second electrode 108 has an opening pattern (slit). Theopening pattern is for generating an electric field in a directiongenerally parallel to the substrate, between the first electrode 102 andthe second electrode 108. Accordingly, as long as an electric fieldhaving a part which is generally parallel to the substrate can begenerated, the opening pattern can have various shapes. Here, “generallyparallel” refers to a parallel direction with small deviation.Therefore, the direction may be deviated from the parallel direction aslong as the display is not disturbed. The direction may have a deviationof, for example, approximately ±10°, or desirably, approximately ±5°.

The opening pattern includes not only a closed opening pattern such as aslit, but also a space which is located between conductive patterns andin which the conductive pattern is not formed, such as a space betweencomb-teeth of a comb-shaped electrode. In other words, a gap or aninterspace is needed between portions functioning as an electrode.

As described above, the electric field is generated between the secondelectrode 108 and the first electrode 102, so that an alignment state ofliquid crystal molecules can be controlled.

Note that in a case where electrodes are provided in each pixel, anelectrode to which a signal different among pixels depending on an imagesignal is provided, that is, a pixel electrode can be either the secondelectrode 108 or the first electrode 102. Accordingly, it is possible toset the second electrode 108 to be the pixel electrode and the firstelectrode 102 to be a common electrode. Alternatively, it is possible toset the second electrode 108 to be the common electrode and the firstelectrode 102 to be the pixel electrode.

Since the pixel electrode is connected to a source or drain of atransistor in many cases, when the first electrode 102 or the secondelectrode 108 functions as the pixel electrode, the structure can besimplified. Further, since the common electrodes in all pixels areconnected to one another in many cases, when the first electrode 102 orthe second electrode 108 functions as the common electrode, thestructure can be simplified.

FIG. 2A is a plan view and FIG. 2B is a cross-sectional view of a casewhere a transistor 201 is provided. The transistor 201 is located nearthe first electrode 102 and the second electrode 108.

In this case, a film in the transistor 201 and the first electrode 102can be formed at the same time. As a result, the first electrode can bemanufactured without increasing the numbers of masks (reticles) andmanufacturing steps.

For example, a semiconductor layer in the transistor 201 and the firstelectrode 102 can be formed at the same time. The semiconductor layer inthe transistor 201 and the first electrode 102 can be formed at the sametime and etched at the same time, whereby patterning can be carried outat the same time. Further, in the case where the semiconductor layer isformed of polysilicon, the semiconductor layer and the first electrode102 are crystallized at the same time.

Accordingly, the semiconductor layer in the transistor 201 and the firstelectrode 102 contain the same material.

Note that in a case of adding an impurity (a p-type impurity or ann-type impurity) such as phosphorus, boron, gallium, or arsenic to apart of the semiconductor layer in the transistor 201, it is desirablethat the impurity is also introduced to the first electrode 102 at thesame time. In a case of adding the impurity at the same time toportions, the concentration thereof is influenced by a thickness and aquality of a material of a film over the portions. When being formedunder the similar layer structures, the semiconductor layer in thetransistor 201 and the first electrode 102 have the impurity (a p-typeimpurity or an n-type impurity) at approximately the same concentration,at least partially. For example, a layer forming a source region or adrain region in the semiconductor layer in the transistor 201 and asemiconductor layer forming the first electrode 102 have impurityregions at approximately the same concentration.

Note that the semiconductor layer in the transistor 201 has a channelforming region in many cases. A gate electrode is located over thechannel forming region with a gate insulating film therebetween. Animpurity (a p-type impurity or an n-type impurity) is not introduced tothe channel forming region to form a high-concentration impurity region,normally. However, there is a case where an impurity (a p-type impurityor an n-type impurity) is introduced to the channel forming region toform an extremely low-impurity region in order to adjust a value of athreshold voltage. Further, an impurity (a p-type impurity or an n-typeimpurity) is introduced to the semiconductor layer in the transistor 201to form a low-concentration impurity region (LDD: Lightly Doped Drain)in some cases. Accordingly, in many cases, the semiconductor layer inthe transistor 201 has a plurality of regions where impurities (p-typeimpurities or n-type impurities) are contained at variousconcentrations.

Note that in a case where an impurity (a p-type impurity or an n-typeimpurity) is introduces to the semiconductor layer in the transistor 201and the first electrode 102 at the same time, the semiconductor layer inthe transistor 201 and the first electrode 102 may be located extremelyclose to each other. It is because the same impurity (a p-type impurityor an n-type impurity) is introduced thereto in many cases. Thus, thelayout of the transistor 201 and the first electrode 102 can besignificantly effective, which leads to improvement in aperture ratio.

Note that the conductivity of a part of the semiconductor layer in thetransistor 201 and that of the first electrode 102 may differ from eachother. In such a case, an impurity (a p-type impurity or an n-typeimpurity) is introduced to the first electrode 102 at the same as atransistor other than the transistor 201. Accordingly, in that case, thesemiconductor layer in the transistor other than the transistor 201 andthe first electrode 102 have the impurity (a p-type impurity or ann-type impurity) at approximately the same concentration, at leastpartially. For example, the transistor other than the transistor 201 isprovided as a part of a source signal line driver circuit or a gatesignal line driver circuit.

The transistor 201 and one of the first electrode 102 and the secondelectrode 108 are electrically connected in many cases. In addition, theelectrode which is electrically connected to the transistor 201functions as the pixel electrode in many cases. The transistor 201 andone of the first electrode 102 and the second electrode 108 areelectrically connected through a contact hole, a wiring, or the like.

Note that in FIGS. 2A and 2B, a case in which the first electrode 102 isformed at the same time as the film in the transistor 201 is described;however, it is not limited thereto. The first electrode 102 may beformed at the same time as another film, such as a film in a wiring, aresistor, or a capacitor.

FIGS. 3A and 3B illustrate a case in which a transistor 301 is providedand a part of the transistor 301 and the first electrode 102 arecontiguous with each other to form one island. FIG. 3A shows a plan viewand FIG. 3B shows a cross-sectional view. Note that in thisspecification, “contiguous” refers to a case in which elements areformed continuously.

At this time, a film in the transistor 301 and the first electrode 102are connected to each other as one film; therefore, they can be formedat the same time. As a result, the first electrode can be manufacturedwithout increasing the numbers of masks (reticles) and manufacturingsteps.

For example, a semiconductor layer in the transistor 301 and the firstelectrode 102 are connected to each other and can be formed at the sametime. The semiconductor layer in the transistor 301 and the firstelectrode 102 can be formed at the same time and etched at the sametime, whereby patterning can be carried out at the same time. Further,if the semiconductor layer is formed of polysilicon, the semiconductorlayer and the first electrode 102 are crystallized at the same time. Inthis case, a crystal grain boundary of the semiconductor layer in thetransistor 301 and that of the semiconductor layer forming the firstelectrode 102 extend in substantially the same direction. Here, thedescription “crystal grain boundaries extend in substantially the samedirection” refers to a case in which, for example, grain boundaries witha longitudinal direction and a direction perpendicular to thelongitudinal direction (also referred to as a short direction) haveuniform longitudinal direction alignment.

Accordingly, the semiconductor layer in the transistor 301 and the firstelectrode 102 contain the same material.

Note that since the semiconductor layer in the transistor 301 and thefirst electrode 102 are contiguous and connected to each other;therefore, in some cases, it is difficult to clearly distinguish wherethe semiconductor layer in the transistor 301 ends and where the firstelectrode 102 begins.

Note that in a case where an impurity (a p-type impurity or an n-typeimpurity) such as phosphorus, boron, gallium, or arsenic is introducedto a part of the semiconductor layer in the transistor 301, it isdesirable that the impurity is also introduced to the first electrode102 at the same time. When the impurity is introduced to thesemiconductor layer in the transistor 301 and the first electrode 102 atthe same time, since they are contiguous with each other, they can beelectrically connected to each other.

In that case, it is not necessary to provide a contact hole and to useanother wiring in order to connect the semiconductor layer in thetransistor 301 and the first electrode 102. Therefore, the layout can besignificantly effective, which leads to improvement in aperture ratio.

Note that since the transistor 301 and the first electrode 102 arecontiguous, they are electrically connected to each other in many cases.The electrode which is electrically connected to the transistor 301functions as the pixel electrode in many cases.

Note that in a case of adding the impurity at the same time to portions,the concentration thereof is influenced by a thickness or a quality of amaterial of a film over the portions. When being formed under thesimilar layer structures, the semiconductor layer in the transistor 301and the first electrode 102 have the impurity (a p-type impurity or ann-type impurity) at approximately the same concentration, at leastpartially.

Note that the semiconductor layer in the transistor 301 has a channelforming region in many cases. A gate electrode is located over thechannel forming region with a gate insulating film therebetween. Animpurity (a p-type impurity or an n-type impurity) is not introduced tothe channel forming region to form a high-concentration impurity region,normally. However, there is a case where an impurity (a p-type impurityor an n-type impurity) is introduced to the channel forming region toform an extremely low-impurity region in order to adjust a value of athreshold voltage. Further, an impurity (a p-type impurity or an n-typeimpurity) is introduced to the semiconductor layer in the transistor 301to form a low-concentration impurity region (LDD: Lightly Doped Drain)in some cases. Accordingly, in many cases, the semiconductor layer inthe transistor 301 has a plurality of regions where impurities (p-typeimpurities or n-type impurities) are contained at variousconcentrations.

Note that the conductivity of a part of the semiconductor layer in thetransistor 301 and that of the first electrode 102 may differ from eachother. In such a case, an impurity (a p-type impurity or an n-typeimpurity) is introduced to the first electrode 102 at the same as atransistor other than the transistor 301. Accordingly, in that case, thesemiconductor layer in the transistor other than the transistor 301 andthe first electrode 102 have the impurity (a p-type impurity or ann-type impurity) at approximately the same concentration, at leastpartially. For example, the transistor other than the transistor 301 isprovided as a part of a source signal line driver circuit or a gatesignal line driver circuit.

The transistor 301 and the first electrode 102 are electricallyconnected in many cases. In addition, the electrode which iselectrically connected to the transistor 301, that is, the firstelectrode 102 functions as the pixel electrode in many cases.Accordingly, the electrode and the transistor can be efficientlylocated, which is favorable.

Note that in FIGS. 3A and 3B, a case in which the first electrode 102 isformed at the same time as the film in the transistor 301 is described;however, it is not limited thereto. The first electrode 102 may beformed at the same time as another film, such as a film in a wiring, aresistor, a capacitor, or the like.

Note that in FIGS. 1A to 3B, a case in which only the second electrode108 has an opening pattern is described, but it is not limited thereto.The first electrode 102 may also have an opening pattern. Accordingly,an electric field generally parallel to the substrate is generated, andorientation of the liquid crystal molecules can be controlled. FIGS. 4Ato 6B show such cases. FIGS. 4A and 4B correspond to a case shown inFIGS. 1A and 1B, in which the first electrode 102 also has an openingpattern. FIGS. 5A and 5B correspond to a case shown in FIGS. 2A and 2B,in which the first electrode 102 also has an opening pattern. FIGS. 6Aand 6B correspond to a case shown in FIGS. 3A and 3B, in which the firstelectrode 102 also has an opening pattern.

When the first electrode 102 has an opening pattern as shown in FIGS. 4Ato 6B, the amount of light transmitting through a portion of the openingpattern is increased. This is because the first electrode 102 and thesecond electrode 108 are not overlapped with each other. When the firstelectrode 102 and the second electrode 108 are overlapped, the amount oflight transmitted therethrough is decreased unless the lighttransmittance is 100%. On the other hand, in a portion where the firstelectrode 102 and the second electrode 108 are not overlapped, lightdoes not attenuate, which leads to increase in amount of lighttransmitted therethrough. As a result, it is possible to increaseluminance and to reduce power consumption.

FIG. 7A is a plan view for illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 1 in the present invention.In FIG. 7A, one of a plurality of pixels provided in the liquid crystaldisplay device is illustrated. This liquid crystal display device is adevice in which an orientation of a liquid crystal is controlled by anFFS mode. In FIG. 7A, a plurality of source wirings 107 a are locatedparallel to one another (extending up and down in FIG. 7A) andseparately from one another, whereas a plurality of gate wirings 104 care located extending in a direction generally perpendicular to thesource wirings 107 a (from side to side in FIG. 7A) and are separatedfrom one another. Auxiliary wirings 104 b are located adjacent to eachof the plurality of gate wirings 104 c and extended to a directiongenerally parallel to the gate wirings 104 c, that is, in a directiongenerally perpendicular (from side to side in FIG. 7A) to the sourcewirings 107 a. A space which is substantially rectangle is surrounded bythe source wiring 107 a, the auxiliary wiring 104 b, and the gate wiring104 c. The pixel electrode of the liquid crystal display device islocated in the space. A thin film transistor for driving the pixelelectrode is located on the upper-left corner of FIG. 7A.

As a material to be used for the gate wiring 104 c, the auxiliary wiring104 b, and the source wiring 107 a, one or more elements selected fromaluminum (Al), tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), neodymium (Nd), chromium (Cr), nickel (Ni), platinum (Pt), gold(Au), silver (Ag), copper (Cu), magnesium (Mg), scandium (Sc), cobalt(Co), zinc (Zn), niobium (Nb), silicon (Si), phosphorus (P), boron (B),arsenic (As), gallium (Ga), indium (In), tin (Sn), and oxygen (O); acompound or an alloy material containing one or more of theaforementioned elements (for example, indium tin oxide (ITO), indiumzinc oxide (IZO), indium tin oxide doped with silicon oxide (ITSO), zincoxide (ZnO), aluminum neodymium (Al—Nd), or magnesium silver (Mg—Ag)); asubstance obtained by combining such compounds; or the like can begiven. Alternatively, a compound (silicide) of silicon and theaforementioned material (such as aluminum silicon, molybdenum silicon,or nickel silicide) or a compound of nitride and the aforementionedmaterial (such as titanium nitride, tantalum nitride, or molybdenumnitride) can be used. Note that silicon (Si) may contain a large amountof n-type impurities (phosphorus or the like) or p-type impurities(boron or the like). When such an impurity is contained, conductivity ofsilicon is improved and silicon functions similarly to normal conductor,so that it becomes easy to use silicon as a wiring or an electrode.Silicon may be single crystalline silicon, polycrystalline silicon(polysilicon), or amorphous silicon. When single crystalline silicon orpolycrystalline silicon is used, resistance can be reduced. Whenamorphous silicon is used, a manufacturing process can be simplified.Aluminum and silver have high conductivity, so that signal delay can bereduced, and minute processing is possible since they are easy to beetched and patterned. Copper has high conductivity, so that signal delaycan be reduced. Molybdenum is desirable because it can be manufacturedwithout a problem such as a defect of a material, even if molybdenum isin contact with an oxide semiconductor such as ITO or IZO, or silicon;and because it is easily patterned and etched, and has high heatresistance. Titanium is desirable because it can be manufactured withouta problem such as a defect of a material, even if titanium is in contactwith an oxide semiconductor such as ITO or IZO, or silicon; and it iseasily patterned and etched, and has high heat resistance. Tungsten isdesirable because it has high heat resistance. Neodymium is desirablebecause it has high heat resistance. In particular, an alloy ofneodymium and aluminum is desirable because heat resistance is improvedand hillocks of aluminum are hardly generated. Silicon is desirablebecause it can be manufactured at the same time as the semiconductorlayer in the transistor and has high heat resistance. Indium tin oxide(ITO), indium zinc oxide (IZO), indium tin oxide doped with siliconoxide (ITSO), zinc oxide (ZnO), and silicon (Si) are desirable becausethey have a light-transmitting property and can be used for a portionwhich is required to transmit light, such as the pixel electrode and thecommon electrode.

Note that a wiring or an electrode may have a single layer or amultilayer structure of these materials. If a single-layer structure isemployed, the manufacturing process can be simplified and the number ofsteps can be reduced; which leads to reduction in cost. If a multilayerstructure is employed, advantage of a material can be derived anddisadvantage of the material can be reduced, so that a wiring and anelectrode with favorable characteristics can be formed. For example,when a material with low resistance (such as aluminum) is included inthe multilayer structure, the resistance of the wiring can be reduced.In addition, if a material with high heat resistance is used, forexample, to be interposed between a material with low heat resistanceand another advantage in a stacked-layer structure, the heat resistanceof wiring or electrode as a whole can be improved. For example, astacked-layer structure in which a layer containing aluminum isinterposed between layers containing molybdenum or titanium isdesirable. In addition, there is a case in which a material is directlyin contact with another wiring or another electrode of another material,so that the materials are adversely affected. For example, a materialmay enter another material and change its characteristics; therefore,the material cannot serve its original purpose or a problem occurs inmanufacturing and the material cannot be manufactured normally. In sucha case, a problem can be solved when the layer is interposed between orcovered with another layer. For example, if indium tin oxide (ITO) andaluminum are required to be in contact with each other, it is desirablethat titanium or molybdenum is interposed therebetween. Also, if siliconand aluminum are required to be in contact with each other, it isdesirable that titanium or molybdenum is interposed therebetween.

Note that it is desirable that the material of the gate wiring 104 c andthe auxiliary wiring 104 b have heat resistance higher than that of thesource wiring 107 a. It is because the gate wiring 104 c and theauxiliary wiring 104 b are located in a higher temperature in theirmanufacturing steps.

Note that it is desirable that the material of the source wiring 107 ahas resistance lower than that of the gate wiring 104 c. It is becauseonly signals of two values, that is, High-signal and Low-signal aregiven to the gate wiring 104 c, whereas an analog signal whichcontributes display is introduced to the source wiring 107 a.Accordingly, it is desirable that a material with low resistance is usedfor the source wiring 107 a so that a signal can be applied withaccuracy thereto.

Note that the auxiliary wiring 104 b is not necessarily provided but apotential of the common electrode in each pixel can be stabilized whenthe auxiliary wiring 104 b is provided. Note that in FIGS. 7A and 7B,the auxiliary wiring 104 b and the gate wiring 104 c are located to begenerally parallel to each other, but it is not limited thereto. Theauxiliary wiring 104 b and the source wiring 107 a may be located to begenerally parallel to each other. In this case, the auxiliary wiring 104b is desirably formed of a material with the same quality as the sourcewiring 107 a.

However, it is favorable that the auxiliary wiring 104 b is locatedgenerally parallel to the gate wiring 104 c because an aperture ratiocan be increased and the layout can be efficient.

FIG. 7B is a cross-sectional view along a line A-B and a line C-D inFIG. 7A. As shown in the drawing, a base insulating film 101 is formedover the substrate 100 so as to prevent diffusion of an impurity fromthe substrate 100. The base insulating film 101 is formed of, forexample, an insulating substance containing oxygen or nitrogen, such assilicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y): x>y), or silicon nitride oxide (SiN_(x)O_(y): x>y).Alternatively, a stacked-layer film including a plurality of filmsthereof may be used.

Note that the substrate 100 is a glass substrate, a quartz substrate, asubstrate formed of an insulator such as alumina, a plastic substratewith enough heat resistance to withstand a processing temperature ofsubsequent steps, a silicon substrate, or a metal substrate.Alternatively, polysilicon may be used.

Note that when the liquid crystal display device functions as atransmissive display device, it is desirable that the substrate 100 hasa light-transmitting property.

A semiconductor film 102 f and a first electrode 102 c controlling theorientation of the liquid crystal are formed over the base insulatingfilm 101. The semiconductor film 102 f and the first electrode 102 care, for example, polysilicon films, which are formed by selectivelyetching a film in the same step. In other words, the semiconductor film102 f and the first electrode 102 c are formed over the baser film 101and in the same layer. However, the present invention is not limited tofilm formation at the same time and etching in one step. In thesemiconductor film 102 f, an impurity region 102 d to be a source regionor a drain region and an impurity region 102 b to be a drain region or asource region of the thin film transistor are formed. The impurityregions 102 d and 102 b are n-type impurity regions to which, forexample, phosphorus or arsenic is introduced, but the impurity regionsmay be p-type impurity regions. An impurity for imparting n-typeconductivity, phosphorus (P) and arsenic (As) are given as an example;and as an impurity for imparting p-type conductivity, boron (B) andgallium (Ga) are given as an example. However, it is desirable that theimpurity regions 102 d and 102 b are n-type impurity regions having highconductivity. On the other hand, when a driver circuit only includesp-type transistors, it is desirable that the impurity regions 102 d and102 b also have p-type conductivity type so that the manufacturing costcan be reduced.

The first electrode 102 c functions as the common electrode to whichcommon voltage which is same as other pixels is applied and is formedof, for example, a polysilicon film to which an impurity is introduced.The resistance of the first electrode 102 is lowered since an impurityis introduced thereto, and functions as an electrode. As shown in adotted line in FIG. 7A, the first electrode 102 c has a rectangularshape with a portion 1001 in which one corner (the upper-left corner ofthe drawing) is lacked, and is formed over almost the whole surface ofthe pixel. Note that in the portion 102 e of which one corner is lacked,a thin film transistor is located. When a thin film transistor islocated in the portion 102 e in which one corner is lacked, a regionwhich can be used to display can be formed more efficiently, which leadsto improvement in aperture ratio. The first electrode 102 c has athickness of, for example, 45 nm to 60 nm, and has sufficiently highlight transmittance. In order to further improve the lighttransmittance, it is desirable to set the thickness of the firstelectrode 102 to be 40 nm or less.

The first electrode 102 c is formed of polysilicon, for example, but maybe another semiconductor material such as amorphous silicon, singlecrystalline silicon, organic semiconductor, or a carbon nanotube. Inthis case, an amorphous silicon film, an organic semiconductor film, orthe like is used in the thin film transistor instead of thesemiconductor film 102 f. Note that the semiconductor film 102 f and thefirst electrode 102 c forming the transistor are desirably formed byselectively etching one film in the same step. In this case, the numbersof masks (reticles) and steps can be reduced, so that the manufacturingcost can be reduced. In addition, it is desirable that impurity elementsof the same type are introduced to the impurity regions 102 b and 102 dat the same time. This is because when the impurity elements of the sametype are introduced, the impurity elements can be introduced without aproblem even if the impurity regions 102 b and 102 d are located closeto each other, so that dense layout becomes possible. It is desirable toadd impurity elements of either p-type or n-type because themanufacturing cost can be low compared with a case in which impurityelements of different types are introduced.

A gate insulating film 103 in the transistor is formed over the wholesurface including over the semiconductor film 102 f.

However, there is a case in which the gate insulating film 103 islocated only in the vicinity of the channel forming region and is notlocated in other parts. In addition, a thickness or a stacked-layerstructure of the gate insulating film 103 may differ according tolocation. For example, the gate insulating film 103 may be thicker orinclude more layers in the vicinity of the channel forming region andmay be thinner or include less layers in another location. Therefore, itbecomes easy to control the addition of an impurity to the source regionor the drain region. Further, when the thickness or the number of layersof the gate insulating film 103 in the vicinity of the channel formingregion differs, the amount of impurity introduced to the semiconductorlayer can be different by location, so that an LDD region or the likecan be formed. When the LDD region is formed, leak current andgeneration of hot carriers can be suppressed, which can improve thereliability.

The gate insulating film 103 is formed of, for example, an insulatingsubstance containing oxygen or nitrogen, such as silicon oxide(SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y):x>y), or silicon nitride oxide (SiN_(x)O_(y): x>y). Alternatively, astacked-layer film including a plurality of these films may be used. Agate electrode 104 a is formed over the gate insulating film 103 and islocated above the channel forming region 102 a. As shown in FIGS. 7A and7B, the gate electrode 104 a is in the same wiring layer as theauxiliary wiring 104 b and the gate wiring 104 c, and is connected tothe gate wiring 104 c. In the semiconductor film 102 f, a region 102 alocated under the gate electrode 104 a functions as a channel formingregion. Note that, to a semiconductor region between the two channelforming regions 102 a, an impurity which is the same as that in theimpurity regions 102 b and 102 d is introduced. Note that in thisembodiment mode, a multigate structure having two gate electrodes isemployed, but the present invention is not limited to this structure.

An insulating film 105 and a first interlayer insulting film 106 a aresequentially formed over the gate insulating film 103 and the gateelectrode 104 a.

Note that only one of the insulating film 105 and the first interlayerinsulating film 106 a may be formed, alternatively, each of theinsulating films has a multilayer structure. An inorganic material or anorganic material can be used for the insulating films. As an organicmaterial, polyimide, acrylic, polyamide, polyimide amide, resist,siloxane, polysilazane, or the like can be used. As an inorganicmaterial, an insulating substance containing oxygen or nitrogen, such assilicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y): x>y), or silicon nitride oxide (SiN_(x)O_(y): x>y) can beused. Alternatively, a stacked-layer film in which a plurality of thesefilms are stacked may be used. Further alternatively, a stacked-layerfilm in which an organic material and an inorganic material are combinedmay be used.

In the gate insulating film 103, the insulating film 105, and the firstinterlayer insulating film 106 a, a contact hole located over theimpurity region 102 b, a contact hole located over the impurity region102 d, a contact hole located over the first electrode 102 c, and acontact hole located over the auxiliary wiring 104 b are formed. Overthe first interlayer insulating film 106 a, the source wiring 107 a, adrain wiring 107 b, and a connection wiring 107 c are formed. When anorganic material is used for the insulating film, intrusion of moistureor an impurity can be prevented. In particular, a layer containingnitrogen can block moisture or an impurity efficiently.

Note that when an organic material is used for the insulating film, asurface thereof can be planarized. Accordingly, the insulating film canhave a good effect on a layer provided thereover. For example, the layerformed over the organic material can be planarized, so that disturbanceof orientation of the liquid crystal can be prevented.

The source wiring 107 a is located above a source, that is, the impurityregion 102 d, and has a part embedded in the contact hole; therefore,the source wiring 107 a and the impurity region 102 d are electricallyconnected. Accordingly, the source electrode functions as a part of thesource wiring 107 a. The drain wiring 107 b is located above a drain,that is, the impurity region 102 b, and has a part embedded in thecontact hole; therefore, the drain wiring 107 b and the impurity region102 b are connected.

The connection wiring 107 c is extended from above the first electrode102 c to above the auxiliary wiring 104 b. The connection wiring 107 chas a part embedded in the contact hole; therefore, the connectionwiring 107 c is electrically connected to both the first electrode 102 cand the auxiliary wiring 104 b. When the connection wiring 107 c isprovided in such a manner, the contact hole can be formed with accuracysince it is not required to be deep.

In the example shown in FIG. 7B, the drain wiring 107 b is formed at thesame time as the source wiring 107 a and the connection wiring 107 c. Inthis case, the contact hole in which a part of the drain wiring 107 b isembedded and the contact hole in which a part of the second electrode108 is embedded is not overlapped with each other. Thus, even if thedrain wiring 107 b and the second electrode 108 have depressions overthe contact holes, the depressions are not overlapped with each other.Therefore, a deep depressed portion is not formed in the secondelectrode 108, so that generation of a defect in shape of the resistpattern formed thereover can be suppressed.

Note that as shown in FIG. 8, the second electrode 108 and the impurityregion 102 b may be connected directly without the drain wiring 107 b.In this case, a contact hole for connecting the second electrode 108 andthe impurity region 102 b is required to be deep. Since the drain wiring107 bb shown in FIG. 7B is not required, a region for the connectionwiring can be utilized for displaying an image as an opening region,which leads to improvement in aperture ratio and reduction in powerconsumption.

As described above, the first electrode 102 c is connected to theauxiliary wiring 104 b through the connection wiring 107 c. It isdesirable that a plurality of connection wirings 107 c are provided inorder to lower the resistance. Thus, a potential of the first electrode102 c is stabilized. In an example shown in FIG. 7A, the connectionwirings 107 c are formed above three corners out of four corners of thefirst electrode 102 c, except the one which is close to the thin filmtransistor. When the connection is made in a plurality of paths,generation of potential distribution in the first electrode 102 c issuppressed. Further, when the first electrode 102 c and the auxiliarywiring 104 b are connected through the connection wiring 107 c, thenumber of forming the contact holes can be reduced, which can simplifythe process.

Note that the connection wiring 107 c is formed at the same time andwith use of the same material as the source wiring 107 a, but it is notlimited thereto. The connection wiring 107 c may be formed at the sametime and with use of the same material as the second electrode 108.

A second interlayer insulating film 106 b is formed over the sourcewiring 107 a, the drain wiring 107 b, the connection wiring 107 c, andthe first interlayer insulating film 106 a. Note that a structure inwhich the second interlayer insulating film 106 b is not formed may beemployed. An inorganic material or an organic material can be used forthe second interlayer insulating film 106 b. As an organic material,polyimide, acrylic, polyamide, polyimide amide, resist, siloxane,polysilazane, or the like can be used. As an inorganic material, aninsulating substance containing oxygen or nitrogen, such as siliconoxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y): x>y), or silicon nitride oxide (SiN_(x)O_(y): x>y) can beused. Alternatively, a stacked-layer film in which a plurality of thesefilms are stacked may be used. Further alternatively, a stacked-layerfilm in which an organic material and an inorganic material are combinedmay be used. In the second interlayer insulating film 106 b, a contacthole is formed over the drain wiring 107 b.

The second electrode 108 which controls the orientation of the liquidcrystal is formed over the interlayer insulating film 106 b. The secondelectrode 108 functions as a pixel electrode to which voltage specificto each pixel is applied. The second electrode 108 is formed of ITO(indium tin oxide), ZnO (zinc oxide), IZO which is formed by using atarget in which ZnO of 2 to 20 wt % is mixed to indium oxide, or thelike. Note that the second electrode 108 and the impurity region 102 bmay be electrically connected through the drain wiring 107 b, or may bedirectly connected.

In a case where the connection wiring is not provided as shown in FIG.8, the second electrode 108 is directly connected to the impurity region102 b in the thin film transistor.

As shown in FIGS. 7A and 8, the second electrode 108 is substantiallyrectangle and located above the first electrode 102 c and thesurroundings thereof. The second electrode 108 has a plurality ofopening patterns 112 in a portion located above the first electrode 102c. The opening patterns 112, for example, include many slit-shapedopening patterns parallel to each other. In the example shown in FIG.7A, the opening patterns are diagonal to the source wiring 107 a. Sincethe opening pattern 112 is provided, an electric field having acomponent parallel to the substrate is generated above the secondelectrode 108. Therefore, the orientation of the liquid crystaldescribed later can be controlled by controlling the potential of thesecond electrode 108. Note that a shape of the opening pattern is notlimited to that in this embodiment mode. A shape of opening patterndescribed in Embodiment Mode 2 or later can be employed. In other words,the opening pattern includes a space where a conductive pattern is notformed, such as a space between the comb-teeth of a comb-shapedelectrode.

If opening patterns with different orientations are provided, aplurality of regions with different moving directions of liquid crystalmolecules can be provided. In other word, a multidomain (also referredto as alignment division) structure can be realized. When a multidomainstructure is employed, it can be prevented that an image cannot bedisplayed properly if seen from a certain direction. Accordingly, theviewing angle can be improved.

As shown in FIG. 7A, a periphery of the first electrode 102 cfunctioning as the common electrode extends out of the second electrode108 functioning as the pixel electrode when seen from a directionperpendicular to the substrate 100. Thus, the second electrode 108 whichis in a floating state after receiving a signal is less influenced by asignal transmitted to another pixel through the source wiring 107 a.Accordingly, a defect of image quality, such as crosstalk can besuppressed. Note that the present invention is not limited to such anelectrode structure and the first electrode 102 c may have a portion inwhich its periphery does not extend out of the second electrode 108.

Next, an alignment film 109 a and a liquid crystal 110 are stacked overthe second interlayer insulating film 106 b and the second electrode108.

As the liquid crystal 110, a ferroelectric liquid crystal (FLC), anematic liquid crystal, a smectic liquid crystal, a liquid crystal whichis to be homogeneously aligned, a liquid crystal which is to behomeotropically aligned, or the like can be used. An opposite substrate111 provided with the second alignment film 109 b is located over theliquid crystal 110. Note that the opposite substrate 111 is providedwith a color filter in many cases. In addition, a polarizing plate isprovided on each outer side of the substrate 100 and the oppositesubstrate 111. Note that a retardation plate or a quarter-wave plate isprovided as well as the polarizing plate in many cases.

Note that a stacked-layer structure according to the present inventionis not limited to the one described in this embodiment mode.

An example of a manufacturing method of a semiconductor device or aliquid crystal display device is described. First, the base insulatingfilm 101 is formed over the substrate 100. Subsequently, a semiconductorfilm such as a polysilicon film or an amorphous silicon film is formedover the base insulating film 101. A resist pattern (not shown) isformed over the semiconductor film. Then, the semiconductor film isselectively etched with use of the resist pattern as a mask. In such amanner, the semiconductor film 102 f and the first electrode 102 c areformed in the same step. The resist pattern is removed thereafter.

Subsequently, the gate insulating film 103 is formed over thesemiconductor film 102 f, the first electrode 102 c, and the baseinsulating film 101. The gate insulating film 103 is, for example, asilicon oxynitride film or a silicon oxide film, and formed by a plasmaCVD method. Note that the gate insulating film 103 may be formed of asilicon nitride film, or a multilayer film containing silicon nitrideand silicon oxide. Then, a conductive film is formed over the gateinsulating film 103. The conductive film is selectively removed byetching using a resist pattern as a mask, and is patterned. Thus, twogate electrodes 104 a are formed over the gate insulating film 103 whichis located over the semiconductor film 102 f. In addition, the auxiliarywiring 104 b and the gate wiring 104 c are formed at the same time asthe gate electrode 104 a.

As described above, the potential of the first electrode 102 c and thesecond electrode 108 in each pixel can be stabilized when the auxiliarywiring 104 b is provided. In addition, the auxiliary wiring 104 b is notnecessarily formed. Alternatively, the auxiliary wiring 104 b may beformed in the same layer as another layer (for example, in the samelayer as the source wiring 107 a, in the same layer as the firstelectrode 102 c, or in the same layer as the second electrode 108) ormay be formed in a plurality of layers. In addition, although in FIG.7A, the auxiliary wiring 104 b extends in the direction perpendicular tothe source wiring 107 a, a structure in which the auxiliary wiring 104 bextends in the same direction as the source wiring 107 a may beemployed.

As a material to be used for the conductive film, one or more elementsselected from aluminum (Al), tantalum (Ta), titanium (Ti), molybdenum(Mo), tungsten (W), neodymium (Nd), chromium (Cr), nickel (Ni), platinum(Pt), gold (Au), silver (Ag), copper (Cu), magnesium (Mg), scandium(Sc), cobalt (Co), zinc (Zn), niobium (Nb), silicon (Si), phosphorus(P), boron (B), arsenic (As), gallium (Ga), indium (In), tin (Sn), andoxygen (O); a compound or an alloy material containing one or more ofthe aforementioned elements (for example, indium tin oxide (ITO), indiumzinc oxide (IZO), indium tin oxide doped with silicon oxide (ITSO), zincoxide (ZnO), aluminum neodymium (Al—Nd), or magnesium silver (Mg—Ag)); asubstance obtained by combining such compounds; or the like can begiven. Alternatively, a compound (silicide) of silicon and theaforementioned material (such as aluminum silicon, molybdenum silicon,or nickel silicide) or a compound of nitride and the aforementionedmaterial (such as titanium nitride, tantalum nitride, or molybdenumnitride) can be used. Note that silicon (Si) may contain a large amountof n-type impurities (phosphorus or the like) or p-type impurities(boron or the like).

Note that the wiring or the electrode may have a single layer or amultilayer structure of these materials. If a single-layer structure isemployed, the manufacturing process can be simplified and the number ofsteps can be reduced; which leads to reduction in cost. If a multilayerstructure is employed, advantage of a material can be derived anddisadvantage of the material can be reduced, so that a wiring and anelectrode with favorable characteristics can be formed. For example,when a material with low resistance (such as aluminum) is included inthe multilayer structure, the resistance of the wiring can be reduced.In addition, if a material with high heat resistance is used, forexample, to be interposed between a material with low heat resistanceand another advantage in a stacked-layer structure, the heat resistanceof the whole wiring or electrode can be improved. For example, astacked-layer structure in which a layer containing aluminum isinterposed between layers containing molybdenum or titanium isdesirable. In addition, there is a case in which a material is directlyin contact with another wiring or another electrode of another material,so that the materials are adversely affected. For example, a materialmay enter another material and change its characteristics; therefore,the material cannot serve its original purpose or a problem occurs inmanufacturing of the material and the material cannot be manufacturednormally. In such a case, a problem can be solved when the layer isinterposed between or covered with another layer. For example, if indiumtin oxide (ITO) and aluminum are in contact with each other, it isdesirable that titanium or molybdenum is interposed therebetween. Also,if silicon and aluminum are in contact with each other, it is desirablethat titanium or molybdenum is interposed therebetween.

Next, an impurity is injected into the semiconductor film 102 f with useof the gate electrode 104 a and a resist pattern (not shown) as a mask.Therefore, the impurity regions 102 b and 102 d and an impurity regionbetween the gate electrodes 104 a are formed. Note that an impurityelement of n-type or p-type may be injected. Alternatively, both ann-type impurity element and a p-type impurity element may be injectedinto a specific region. In the latter case, it is set so that theinjected amount of either the n-type impurity element or the p-typeimpurity element is more than the other.

Note that at this time, an LDD region may be formed by changing thethickness or the stacked-layer structure of the gate insulating film103. In order to form the LDD region, the gate insulating film isthickened or the number of layers is increased in a portion in which theLDD region is to be formed. Accordingly, the injected amount of theimpurity is decreased, so that the LDD region can be easily formed.

Note that the resist pattern may be used as a mask in this step.

In addition, in a step of forming the impurity region, an impurityelement may be injected into the first electrode 102 c. In such amanner, the first electrode 102 c can be formed at the same time as theimpurity regions 102 b and 102 d. Therefore, the number of steps is notincreased, so that the manufacturing cost of the liquid crystal displaydevice can be low.

Note that the injection of the impurity element into the impurity regionmay be carried out before forming the gate electrode 104 a, for example,before or after forming the gate insulating film 103. In that case, theimpurity element is injected with use of the resist pattern as a mask.At this time, the impurity element may be injected into the firstelectrode 102 c. Also in this case, the step of forming the impurityregion in the transistor and the step of injecting the impurity elementinto the first electrode 102 c can be the same step. Accordingly, themanufacturing cost of the liquid crystal display device can be low.

Further, in this case, a capacitor can be formed between an electrode inthe same layer as the gate and the semiconductor film into which theimpurity is injected. Since the gate insulating film is located betweenthe electrode in the same layer as the gate and the semiconductor filminto which the impurity is injected, a capacitor with thin thickness andlarge capacity can be formed.

Then, the first interlayer insulating film 106 a and the contact holesare formed. Subsequently, a conductive film (such as a metal film) isformed over the first interlayer insulating film 106 a and in thecontact holes. The metal film is patterned, in other words, selectivelyremoved. Thus, the source wiring 107 a, the drain wiring 107 b, and theconnection wiring 107 c are formed. As described above, the conductivefilm can be formed of various materials to have various structures. Forexample, a film formed of aluminum (Al), nickel (Ni), tungsten (W),molybdenum (Mo), titanium (Ti), tantalum (Ta), neodymium (Nd), platinum(Pt), gold (Au), silver (Ag), or the like; a film formed of an alloythereof; or a stacked-layer film thereof can be used. Alternatively,silicon (Si) to which an n-type impurity is introduced may be used.

Then, the second interlayer insulating film 106 b and the contact holesare formed. Thereafter, an ITO film, an IZO film, or a ZnO film isformed over the second interlayer insulating film 106 b and in thecontact holes. The film is selectively etched with use of a resistpattern. Thus, the second electrode 108 is formed.

Note that the contact hole in which a part of the drain wiring 107 b isembedded and the contact hole in which a part of the second electrode108 is embedded are different from each other in location. Thus, even ifthe drain wiring 107 b and the second electrode 108 have depressions inportions located over the contact holes, the depressions are notoverlapped with each other. Therefore, a deep depressed portion is notformed in the second electrode 108, so that generation of a defect inshape of the aforementioned resist pattern can be suppressed.Thereafter, the resist pattern is removed.

However, the present invention is not limited thereto. For example, thecontact hole in which a part of the drain wiring 107 b is embedded andthe contact hole in which a part of the second electrode 108 is embeddedmay be overlapped with each other. In this case, the contact holes canbe accommodated in one location, therefore the layout can be efficient.Accordingly, the aperture ratio can be improved.

Subsequently, the first alignment film 109 a is formed, and the liquidcrystal is sealed between the first alignment film 109 a and theopposite substrate 111 provided with the second alignment film 109 b.Thereafter, on a side of the opposite substrate 111 or on a side of thesubstrate 100 which are not in contact with the liquid crystal 110 (thatis, an outer side of the liquid crystal display device), an optical filmor the like such as a polarizing plate, a retardation plate, aquarter-wave plate, a diffusing plate, or a prism sheet is provided.Further, a backlight or a frontlight is provided. As the backlight, adirect type or a sidelight type can be used. As a light source, a coldcathode tube or an LED (light emitting diode) can be used. As the LED,white color LED or single color LED (such as white, red, blue, green,cyan, magenta, or yellow) may be combined to be used. When the LED isused, color purity can be improved since the LED has a sharp peak oflight wavelength. In such a manner, a liquid crystal display device isformed.

Note that a liquid crystal display device may only refer to a substrate,an opposite substrate, and a liquid crystal interposed therebetween.Alternatively, a liquid crystal display device may further include anoptical film such as a polarizing plate or a retardation plate. Furtheralternatively, a liquid crystal display device may further include adiffusing plate, a prism sheet, a light source (such as a cold cathodetube or an LED), a light-guide plate, and the like.

According to Embodiment Mode 1 in the present invention, in the liquidcrystal display device in which the alignment direction of the liquidcrystal is controlled by an FFS mode, the first electrode 102 c isformed of a polysilicon film to which an impurity is introduced, andformed in the same step as the semiconductor film 102 f including thesource region, the drain region, and the channel forming region of thethin film transistor. Therefore, the number of manufacturing steps andthe manufacturing cost can be reduced compared with a case in which thecommon electrode is formed of ITO.

Although the connection wiring 107 c is located in the same layer as thesource wiring 107 a and the drain wiring 107 b in this embodiment mode,the connection wiring 107 c may be located in another wiring layer (forexample, in the same layer as the gate wiring 104 c, the first electrode102 c, or the second electrode 108). In addition, the gate insulatingfilm 103 is not necessarily formed over the whole surface.

The auxiliary wiring 104 b may be formed in the same layer as the sourcewiring 107 a. In this case, the auxiliary wiring 104 b may be locatedparallel to the gate wiring 104 c, and the auxiliary wiring 104 b andthe gate wiring 104 c may be formed in the same layer only in a portionin which the source wiring 107 a and the auxiliary wiring 104 b areintersected. Alternatively, the auxiliary wiring 104 b and the sourcewiring 107 a may be located in parallel.

The gate electrode 104 a and the gate wiring 104 c may be formed ofdifferent materials or in the different layers.

Although a so-called top gate thin film transistor in which the gateelectrode is located above the channel forming region is described inthis embodiment mode, the present invention is not particularly limitedthereto. A so-called bottom gate thin film transistor in which the gateelectrode is located under the channel forming region or a transistorhaving a structure in which the gate electrodes are located over andunder the channel forming region may be formed.

Embodiment Mode 2

FIG. 9A is a plan view illustrating a structure of an FFS mode liquidcrystal display device according to Embodiment Mode 2 in the presentinvention. FIG. 9B is a cross-sectional view along a line A-B and a lineC-D of FIG. 9A. A structure of this embodiment mode is similar to thatof Embodiment Mode 1, except that the first electrode 102 c iselectrically connected to the source wiring 107 a through the transistorand functions as the pixel electrode, the second electrode 108 iselectrically connected to the auxiliary wiring 104 b and functions asthe common electrode, a shape of the opening pattern 112 formed in thesecond electrode 108 is different, and connection structures of thefirst electrode 102 c, the second electrode 108, and the wirings aredifferent. Also, a manufacturing method of the liquid crystal displaydevice according to this embodiment mode is almost similar to that inEmbodiment Mode 1. Therefore, the description in Embodiment Mode 1 canbe applied to this embodiment mode. Hereinafter, the component similarto that of Embodiment Mode 1 is denoted by the same reference numeraland description thereof is omitted.

The impurity region 102 b to be a drain or a source of the transistor isdirectly connected to the first electrode 102 c. In other words, thesemiconductor layer in the transistor and the first electrode 102 c arecontiguous with each other to form one island. In addition, unlikeEmbodiment Mode 1, the contact hole located over the impurity region 102b and the contact hole located over the first electrode 102 c are notformed in the first interlayer insulating film 106 a. Accordingly, theregion for the contact holes can be utilized for displaying an image,which leads to improvement in aperture ratio.

Note that since the impurity region 102 b functioning as the drain orthe source of the transistor and the first electrode 102 are contiguousand connected to each other; therefore, in some cases, it is difficultto clearly see where the impurity region 102 b in the transistor endsand where the first electrode 102 begins.

Note that in a case where an impurity (a p-type impurity or an n-typeimpurity) such as phosphorus, boron, gallium, or arsenic is introducedto the impurity region to be as the drain or the source of thetransistor, it is desirable that an impurity having the sameconductivity is also introduced to the first electrode 102 c at the sametime. When the impurity is introduced to the impurity region and thefirst electrode 102 c at the same time, since they are contiguous witheach other, they can be electrically connected to each other. At thistime, the concentration of the impurity introduced to portions isinfluenced by a thickness or a quality of a material of the film overthe portions. When being formed under the similar layer structures, theimpurity region functioning as a drain or a source of the transistor andthe first electrode 102 c have the impurity (a p-type impurity or ann-type impurity) at approximately the same concentration, at leastpartially.

A contact hole located over the connection wiring 107 c is formed in thesecond interlayer insulating film 106 b. The second electrode 108 has apart embedded in the contact hole, so as to be connected to theconnection wiring 107 c.

As shown in FIG. 9A, in this embodiment mode, the second electrode 108has two kinds of opening patterns 112 a and 112 b. The opening pattern112 a formed in an upper region in the drawing and the opening pattern112 b formed in a lower region in the drawing have differentorientations from each other.

If opening patterns 112 a and 112 b with different orientations areprovided, a plurality of regions with different moving directions ofliquid crystal molecules can be realized. In other word, a multidomainstructure can be employed. When a multidomain structure is employed, itcan be prevented that an image cannot be displayed properly if seen froma certain direction. Accordingly, the viewing angle can be improved.

In addition, as shown in FIGS. 9A and 9B, the first electrode 102 cfunctions as the pixel electrode and the second electrode 108 functionsas the common electrode, and the liquid crystal is located closer to thecommon electrode than to the pixel electrode. Accordingly, even ifvoltage of the pixel electrode varies among pixels, an electric field ina portion where the liquid crystal exists hardly changes due to animage; therefore, adjacent pixels are less affected each other, so thatcrosstalk can be reduced.

With this embodiment mode, an effect similar to Embodiment Mode 1 can beobtained. In addition, the opening patterns 112 a and 112 b withdifferent orientations are formed in the second electrode 108.Therefore, the direction of electrical field gradient generated betweenthe first electrode 102 c and the second electrode 108 and in the liquidcrystal 110 can be divided into two in a plane parallel to thesubstrate. Therefore, the viewing angle of the liquid crystal displaydevice can be further improved.

Note that in Embodiment Mode 1, the shape of the second electrode 108may be similar to that in this embodiment mode. In addition, in thisembodiment mode, the shape of the opening pattern in the secondelectrode 108 may be similar to that in Embodiment Mode 1. Although onlyone pixel is shown in FIGS. 9A and 9B, a plurality of pixels arearranged in matrix in practice. In practice, the second electrodes 108in pixels may be connected to each other through the connection wiring107 c. Accordingly, the resistance can be lowered, so that thesufficient voltage can be applied to the second electrode 108.

Note that this embodiment mode shows an example in a case in which thedescription in Embodiment Mode 1 is partially changed, improved, ortransformed. Therefore, the description in Embodiment Mode 1 can beapplied to or combined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 3

FIG. 10A is a plan view illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 3 in the present invention.FIG. 10B is a cross-sectional view along a line A-B, a line C-D, and aline E-F of FIG. 10A. A structure of this embodiment mode is similar tothat of Embodiment Mode 1, except that an opening pattern 115 is formedin the first electrode 102 c and except for the shape of the openingpattern 112. In other words, the liquid crystal display device accordingto this embodiment mode is a device in which the alignment direction ofthe liquid crystal is controlled by an IPS mode. The pixel portion andthe common electrode are alternately arranged and are generally inparallel in a main portion, when seen from a direction perpendicular tothe substrate 100 of the liquid crystal display device. In theaforementioned FFS mode, a lower electrode of the pixel electrode andthe common electrode does not have an opening pattern. Note that amanufacturing method of the liquid crystal display device according tothis embodiment mode is generally similar to that of Embodiment Mode 1.Accordingly, the description in Embodiment Mode 1 can be applied to thisembodiment mode. Hereinafter, the component similar to that ofEmbodiment Mode 1 is denoted by the same reference numeral anddescription thereof is omitted.

The opening pattern 115 is located under a region of the secondelectrode 108, in which the opening pattern 112 is not formed, and thesurroundings thereof. Accordingly, the first electrode 102 c functioningas the common electrode and the second electrode 108 functioning as thepixel electrode are alternately arranged and generally parallel exceptin the periphery portions. With the aforementioned electrode structure,an electric field parallel to the substrate can be generated between thefirst electrode 102 c and the second electrode 108, and an effect suchas improvement in viewing angle which is characteristics of an IPS modecan be obtained. The opening patterns 112 and 115 have wave-shapes inthis embodiment mode.

If the opening patterns are thus provided to have differentorientations, a plurality of regions with different moving directions ofliquid crystal molecules can be realized. In other word, a multidomainstructure can be employed. When a multidomain structure is employed, itcan be prevented that an image cannot be displayed properly if seen froma certain direction. Accordingly, the viewing angle can be improved.

In this embodiment mode, a portion of the first electrode 102 c and aportion of the second electrode 108 (portions denoted by referencenumerals 120 a and 120 b) interpose the gate insulating film 103, theinsulating film 105, the first interlayer insulating film 106 a, and thesecond interlayer insulating film 106 b. Therefore, in each portiondenoted by the reference numerals 120 a and 120 b, the first electrode102 c, the second electrode 108, and the insulating film therebetweenfunction as a capacitor. With provision of the capacitors 120 a and 120b, the storage capacitance can be increased. Therefore, when a thin filmtransistor is turned off, the potential of the second electrode 108 canbe easily kept.

With this embodiment mode, an effect similar to Embodiment Mode 1 can beobtained. Note that in this embodiment mode, the opening pattern 112formed in the second electrode 108 may have the shape of the openingpattern 112 shown in FIGS. 7A and 7B or 9A and 9B. In this case, theopening pattern 115 included in the first electrode 102 c has a shapesimilar to the opening pattern 112 shown in FIGS. 7A and 7B, or 9A and9B. Note that the opening patterns 112 and 115 are required to bearranged so that the first electrode 102 c and the second electrode 108are alternately arranged and are generally in parallel except in theperiphery portions, when seen from the direction perpendicular to thesubstrate 100 of the liquid crystal display device.

In addition, in Embodiment Mode 1 or 2, the opening pattern 112 may havea shape similar to that in this embodiment mode. In this case, an FFSmode liquid crystal display device in which the opening pattern 112 hasthe shape shown in FIGS. 10A and 10B can be obtained.

Note that the first electrode 102 c has the opening pattern 115 in thisembodiment mode. Therefore, in a portion of the opening pattern, theamount of light transmitted therethrough is increased. This is becausethe first electrode 102 is not provided in that portion. In a portionwhere the first electrode 102 is provided, the amount of lighttransmitted therethrough is decreased because the light transmittance isnot 100%. On the other hand, in a portion where the first electrode 102is not provided, the light does not attenuate, which leads to increasein amount of light transmitted therethrough. As a result, it is possibleto increase luminance and to reduce power consumption.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 and 2 is partially changed, improved,or transformed. Therefore, the description in Embodiment Modes 1 and 2can be applied to or combined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 4

FIG. 11A is a plan view illustrating a structure of an IPS mode liquidcrystal display device according to Embodiment Mode 4 in the presentinvention. FIG. 11B is a cross-sectional view along a line A-B and aline C-D of FIG. 11A. A structure in this embodiment mode is similar toEmbodiment Mode 2, except that the opening pattern 115 is formed in thefirst electrode 102 c and except for the shape of the opening pattern112. Also, a manufacturing method of the liquid crystal display deviceaccording to this embodiment mode is generally similar to that inEmbodiment Mode 2. Accordingly, the description in Embodiment Mode 2 canbe applied to this embodiment mode. Hereinafter, the component similarto that of Embodiment Mode 2 is denoted by the same reference numeraland description thereof is omitted.

The impurity region 102 b to be a drain or a source of the transistor isdirectly connected to the first electrode 102 c. In other words, thesemiconductor layer in the transistor and the first electrode 102 c arecontiguous with each other to form one island. In addition, unlikeEmbodiment Mode 1, the contact hole located over the impurity region 102b and the contact hole located over the first electrode 102 c are notformed in the first interlayer insulating film 106 a. Accordingly, theregion for the contact holes can be utilized for displaying an image,which leads to improvement in aperture ratio.

The opening pattern 115 is located under a region of the secondelectrode 108, in which the opening pattern 112 is not formed and thesurroundings thereof. Accordingly, the first electrode 102 c functioningas the pixel electrode and the second electrode 108 functioning as thecommon electrode are alternately arranged and are generally in parallelexcept in the periphery portions. With the aforementioned electrodestructure, a lateral electric field can be generated between the firstelectrode 102 c and the second electrode 108, and an effect such asimprovement in viewing angle which is characteristics of an IPS mode canbe obtained. The opening patterns 112 and 115 are generally parallel tothe source wiring 107 a in this embodiment mode.

In this embodiment mode, a portion of the first electrode 102 c and aportion of the second electrode 108 (portions denoted by referencenumerals 121 a and 121 b) interpose the gate insulating film 103, theinsulating film 105, the first interlayer insulating film 106 a, and thesecond interlayer insulating film 106 b. Therefore, in each portiondenoted by the reference numerals 121 a and 121 b, the first electrode102 c, the second electrode 108, and the insulating film therebetweenfunction as a capacitor. With provision of the capacitors 121 a and 121b, the storage capacitance can be increased. Therefore, when a thin filmtransistor is turned off, the potential of the first electrode 102 c canbe easily kept.

In this embodiment mode, an effect similar to Embodiment Mode 1 can beobtained. Note that in this embodiment mode, the opening patterns 112and 115 may have the shape shown in FIGS. 10A and 10B. Alternatively,the opening pattern 112 may have the shape shown in FIGS. 7A and 7B, or9A and 9B. In this case, the opening pattern 115 has a shape similar tothe opening pattern 112 shown in FIGS. 7A and 7B, or 9A and 9B. Notethat the opening patterns 112 and 115 are required to be arranged sothat the first electrode 102 c and the second electrode 108 arealternately arranged and are generally in parallel except in theperiphery portions, when seen from the direction perpendicular to thesubstrate 100 of the liquid crystal display device.

In addition, the opening patterns 112 and 115 in the IPS mode liquidcrystal display device shown in Embodiment Mode 3 may have the shapeshown in FIGS. 11A and 11B. Alternatively, in Embodiment Mode 1 or 2,the opening pattern 112 may have a shape similar to that in thisembodiment mode. In the latter case, an FFS mode liquid crystal displaydevice in which the opening pattern 112 has the shape shown in FIGS. 11Aand 11B can be obtained.

Note that the first electrode 102 c has the opening pattern 115 in thisembodiment mode. Therefore, in a portion of the opening pattern, theamount of light transmitted therethrough is increased. This is becausethe first electrode 102 is not provided in that portion. In a portionwhere the first electrode 102 is provided, the amount of lighttransmitted therethrough is decreased because the light transmittance isnot 100%. On the other hand, in a portion where the first electrode 102is not provided, the light does not attenuate, which leads to increasein the amount of light transmitted therethrough. As a result, it ispossible to increase luminance and to reduce power consumption.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 3 is partially changed, improved,or transformed. Therefore, the description in Embodiment Modes 1 to 3can be applied to or combined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 5

FIG. 12A is a plan view illustrating a structure of an FFS mode liquidcrystal display device according to Embodiment Mode 5 in the presentinvention. FIG. 12B is a cross-sectional view along a line A-B and aline C-D of FIG. 12A. A structure of this embodiment mode is similar tothat of Embodiment Mode 1, except that the second interlayer insulatingfilm 106 b is not formed, and the second electrode 108 is formed overthe first interlayer insulating film 106 a. A part of the secondelectrode 108 is located over the drain wiring 107 b and the secondelectrode 108 and the drain wiring 107 b are directly connectedtherethrough.

The second electrode 108 is formed after the source wiring 107 a, thedrain wiring 107 b, and the connection wiring 107 c are formed. Byforming the second electrode 108 after forming the drain wiring 107 b,residue of etching of the drain wiring 107 b is prevented from remainingon a surface of the second electrode 108, which can planarize thesurface of the second electrode 108. Note that a structure in which thesecond electrode 108 covers the drain wiring 107 b may be employed.

Note that the second electrode 108 may be formed at the same time as thesource wiring 107 a and the drain wiring 107 b. That is, they may beformed of a similar material and by patterning at the same time.Accordingly, a step of forming a light-transmitting electrode can beomitted, so that the cost can be reduced.

Therefore, the second electrode 108 does not necessarily have alight-transmitting property. In other words, the second electrode 108may reflect light.

A manufacturing method of the liquid crystal display device according tothis embodiment mode is generally similar to that in Embodiment Mode 1,except that the step of forming the second interlayer insulating film106 b is omitted. Therefore, the description in Embodiment Mode 1 can beapplied to this embodiment mode. Note that since the step of forming thesecond interlayer insulating film 106 b is omitted, the manufacturingcost of the liquid crystal display device is lowered. Hereinafter, thecomponent similar to that of Embodiment Mode 1 is denoted by the samereference numeral and description thereof is omitted.

With this embodiment mode, an effect similar to Embodiment Mode 1 can beobtained. Note that in this embodiment mode, the number of theinterlayer insulating films is smaller by one than that of EmbodimentMode 1, an electrical field gradient between the first electrode 102 cand the second electrode 108 becomes large. Therefore, a potentialgradient of the same level can be obtained with low voltage, wherebypower consumption of the liquid crystal display device can be reduced.This effect is enhanced when the first interlayer insulating film 106 ais formed of a material with high dielectric constant (such as siliconnitride, aluminum oxide, hafnium oxide, or tantalum oxide). In the caseof forming the first interlayer insulating film 106 a of a material withhigh dielectric constant, an effect in which storage capacitance can beincreased can be also obtained. In addition, since the step of formingthe second interlayer insulating film 106 b is omitted, themanufacturing cost is low compared with Embodiment Mode 1.

Note that in this embodiment mode, a structure similar to EmbodimentMode 2 may be employed, in which the first electrode 102 c and theimpurity region 102 b to be a drain may be connected, so that the firstelectrode 102 c may function as the pixel electrode. In this case, thereis an advantage over Embodiment Mode 2 in that the second interlayerinsulating film 106 b is not required. In addition, the second electrode108 is directly connected to the connection wiring 107 c in the samemanner of the drain wiring 107 b and the second electrode 108 in FIGS.12A and 12B where the second electrode 108 is partially located over thedrain wiring 107 b. Thus, the second electrode 108 functions as thecommon electrode.

In this embodiment mode, the second electrode 108 and the openingpattern 112 may have the shapes shown in FIGS. 9A and 9B, 10A and 10B,or 11A and 11B. If the second electrode 108 and the opening pattern 112have the shapes shown in FIGS. 10A and 10B, or 11A and 11B, thecapacitors denoted by the reference numerals 120 a and 120 b in FIGS.10A and 10B or the capacitors denoted by the reference numerals 121 aand 121 b in FIGS. 11A and 11B are formed, so that the storagecapacitance can be increased. Therefore, when a thin film transistor isturned off, the potential of the second electrode 108 can be easilykept.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 4 is partially changed, improved,or transformed. Therefore, the description in Embodiment Modes 1 to 4can be applied to or combined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 6

FIG. 13A is a plan view illustrating a structure of an IPS mode liquidcrystal display device according to Embodiment Mode 6 in the presentinvention. FIG. 13B is a cross-sectional view along a line A-B, a lineC-D, and a line E-F of FIG. 13A. A liquid crystal display deviceaccording to this embodiment mode is similar to that of Embodiment Mode3, except that a capacitor 114 connected to the second electrode 108 isprovided. Note that as long as a structure in which the capacitor isconnected to the auxiliary wiring 104 b and the second electrode 108,the present invention is not limited to the structure shown in thisembodiment mode. In addition, a manufacturing method of the liquidcrystal display device according to this embodiment mode is generallysimilar to that in Embodiment Mode 3. Therefore, the description inEmbodiment Mode 3 can be applied to this embodiment mode. Hereinafter,the component similar to that of Embodiment Mode 3 is denoted by thesame reference numeral and description thereof is omitted.

An electrode 113 for the capacitor which is located above the auxiliarywiring 104 b is formed over the first interlayer insulating film 106 a.The electrode 113 for the capacitor is located in the same layer as thesource wiring 107 a and formed in the same step as the source wiring 107a. The capacitor 114 includes the auxiliary wiring 104 b and theelectrode 113 for the capacitor with the insulating film 105 and thefirst interlayer insulating film 106 a therebetween. Since the capacitoris formed above the auxiliary wiring 104 b, an area of the openingportion is not reduced. Therefore, in a case of providing the capacitor,the aperture ratio is not decreased.

A contact hole located over the electrode 113 for the capacitor isformed in the second interlayer insulating film 106 b. The secondelectrode 108 has a part embedded in the contact hole, so as to beconnected to the electrode 113 for the capacitor.

With this embodiment mode, an effect similar to Embodiment Mode 3 can beobtained. In addition, since the capacitor 114 is connected between thesecond electrode 108 functioning as a pixel electrode and the auxiliarywiring 104 b, the voltage of the second electrode 108 is easily keptwhen the thin film transistor is turned off.

Note that in this embodiment mode, the opening patterns 112 and 115 mayhave the shape shown in FIGS. 11A and 11B. Alternatively, the openingpattern 112 may have the shape shown in FIGS. 7A and 7B, or 9A and 9B.In this case, the opening pattern 115 in the first electrode 102 c mayhave a shape similar to the opening pattern 112 shown in FIGS. 7A and7B, or 9A and 9B. Note that the opening patterns 112 and 115 arerequired to be arranged so that the first electrode 102 c and the secondelectrode 108 are alternately arranged and are generally in parallelexcept in the periphery portions, when seen from the directionperpendicular to the substrate 100 of the liquid crystal display device.

In Embodiment Mode 1 shown in FIGS. 7A and 7B, an effect similar to thisembodiment mode can be obtained if the capacitor 114 is formed andconnected to the second electrode 108. In addition, if the electrode 113for the capacitor is located above the gate wiring 104 c, a similareffect can be obtained because the potential of the gate wiring 104 c issubstantially constant when the pixel is not selected. The capacitor maykeep the potential of the pixel electrode; therefore, the capacitor ispreferably formed between the pixel electrode and a wiring with aconstant potential. It is more preferable that the gate wiring 104 cconnected to the capacitor is the gate wiring in one preceding rowbecause the potential thereof is substantially constant since itsselected state is finished.

If the opening patterns are thus provided to have different orientationsand shapes, a plurality of regions with different moving directions ofliquid crystal molecules can be provided. In other word, a multidomainstructure can be realized. When a multidomain structure is employed, itcan be prevented that an image cannot be displayed properly if seen froma certain direction. Accordingly, the viewing angle can be improved.

Note that the first electrode 102 c has the opening pattern 115 in thisembodiment mode. Therefore, in a portion of the opening pattern, theamount of light transmitted therethrough is increased. This is becausethe first electrode 102 is not provided in that portion. In a portionwhere the first electrode 102 is provided, the amount of lighttransmitted therethrough is decreased because the light transmittance isnot 100%. On the other hand, in a portion where the first electrode 102is not provided, light does not attenuate, which leads to increase inamount of light transmitted therethrough. As a result, it is possible toincrease luminance and to reduce power consumption.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 5 is partially changed, improved,or transformed. Therefore, the description in Embodiment Modes 1 to 5can be applied to or combined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 7

FIG. 14A is a plan view illustrating a structure of an IPS mode liquidcrystal display device according to Embodiment Mode 7 in the presentinvention. FIG. 14B is a cross-sectional view along a line A-B, a lineC-D, and a line E-F of FIG. 14A. A structure in this embodiment mode issimilar to that of the IPS mode liquid crystal display device accordingto Embodiment Mode 4, except that the opening patterns 115 and 112 havea substantially V-shape and the capacitor 117 electrically connected tothe first electrode 102 c, and the auxiliary wiring 104 b is provided.Accordingly, the description in Embodiment Mode 4 can be applied to thisembodiment mode. Hereinafter, the component similar to that ofEmbodiment Mode 4 is denoted by the same reference numeral anddescription thereof is omitted.

The capacitance 117 is formed when a part of the first electrode 102 c(a lower end in FIG. 14A) is located under the auxiliary wiring 104 b.In other words, the capacitance 117 includes the first electrode 102 c,the auxiliary wiring 104 b, and the gate insulating film 103therebetween.

A manufacturing method of a liquid crystal display device according tothis embodiment mode is similar to Embodiment Mode 3, except that theimpurity is injected into the first electrode 102 c before forming aconductive film to be the auxiliary wiring 104 b, and the impurity isinjected into the semiconductor film 102 f after forming the gateelectrode 104 a, the auxiliary wiring 104 b, and the like. Accordingly,the resistance of a whole part of the first electrode 102 c, which formsthe capacitor 117, is lowered and the capacitor 117 operates only bychanging the potential of the first electrode 102 c with respect to theauxiliary wiring 104 b.

With this embodiment mode, an effect similar to Embodiment Mode 4 can beobtained. In addition, since the capacitor 117 is connected between thefirst electrode 102 c functioning as the pixel electrode and theauxiliary wiring 104 b, the voltage of the second electrode 102 c iseasily kept when the thin film transistor is turned off.

Note that the capacitor 117 may be provided in Embodiment Mode 2. Inthis case, an effect similar to this embodiment mode can be obtained.

In this embodiment mode, the opening patterns 112 and 115 may have theshape shown in FIGS. 10A and 10B, or 11A and 11B. Alternatively, theopening pattern 112 may have the shape shown in FIGS. 7A and 7B, or 9Aand 9B. In this case, the opening pattern 115 has the shape of theopening pattern 112 shown in FIGS. 7A and 7B, or 9A and 9B. Note thatthe opening patterns 112 and 115 are required to be arranged so that thefirst electrode 102 c and the second electrode 108 are alternatelyarranged and generally in parallel except in the periphery portions,when seen from the direction perpendicular to the substrate 100 of theliquid crystal display device.

In the IPS mode liquid crystal display device according to Embodimentmode 3, 4, or 6, the opening patterns 112 and 115 may have the shapeshown in FIGS. 14A and 14B. In addition, in the FFS mode liquid crystaldisplay device according to Embodiment mode 1, 2, or 5, the openingpattern 112 may have the shape shown in FIGS. 14A and 14B.

The impurity region 102 b functioning as a drain or a source of thetransistor is directly connected to the first electrode 102 c. In otherwords, the semiconductor layer in the transistor and the first electrode102 c are contiguous with each other to form one island. In addition,unlike Embodiment Mode 1, the contact hole located over the impurityregion 102 b and the contact hole located over the first electrode 102 care not formed in the first interlayer insulating film 106 a.Accordingly, the region for the contact holes can be utilized fordisplaying an image, which leads to improvement in aperture ratio.

If the opening patterns are thus provided to have differentorientations, a plurality of regions with different moving directions ofliquid crystal molecules can be provided. In other word, a multidomainstructure can be realized. When a multidomain structure is employed, itcan be prevented that an image cannot be displayed properly if seen froma certain direction. Accordingly, the viewing angle can be improved.

Note that the first electrode 102 c has the opening pattern 115 in thisembodiment mode. Therefore, in a portion of the opening pattern, theamount of light transmitted therethrough is increased. This is becausethe first electrode 102 is not provided in that portion. In a portionwhere the first electrode 102 is provided, the amount of lighttransmitted therethrough is decreased because the light transmittance isnot 100%. On the other hand, in a portion where the first electrode 102is not provided, light does not attenuate, which leads to increase inamount of light transmitted therethrough. As a result, it is possible toincrease luminance and to reduce power consumption.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 6 is partially changed, improved,or transformed. Therefore, the description in Embodiment Modes 1 to 6can be applied to or combined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 8

FIG. 15A is a plan view illustrating a structure of an IPS mode liquidcrystal display device according to Embodiment Mode 8 in the presentinvention. FIG. 15B is a cross-sectional view along a line A-B, a lineC-D, and a line E-F of FIG. 15A. A structure in this embodiment mode issimilar to that of the IPS mode liquid crystal display device accordingto Embodiment Mode 3, except that a capacitor 118 is provided instead ofthe capacitor 120 b, a second auxiliary wiring 104 e is formed, and theopening patterns 112 and 115 have substantially V-shapes. Accordingly,the description in Embodiment Mode 3 can be applied to this embodimentmode. Hereinafter, the component similar to that of Embodiment Mode 3 isdenoted by the same reference numeral and description thereof isomitted.

The capacitor 118 is connected between the second electrode 108 and thesecond auxiliary wiring 104 e. The capacitor 118 includes thesemiconductor film 102 e located over the base insulating film 101, thegate insulating film 103 located over the semiconductor film 102 e, anda conductive pattern 104 d which is formed over the gate insulating film103 and located above a part of the semiconductor film 102 e. Thecapacitor 118 is located so as not to overlap with the first electrode102 c. The semiconductor film 102 e and the conductive pattern 104 d arerectangles and are located adjacent to and generally parallel to theauxiliary wiring 104 b. The same impurity as in the first electrode 102c is introduced to the semiconductor film 102 e except in the regionunder the conductive pattern 104 d.

The contact hole located above the conductive pattern 104 d and thecontact hole located above the semiconductor film 102 e are formed inthe first interlayer insulating film 106 a. Conductive patterns 107 dand 107 e are formed over the first interlayer insulating film 106 a.The conductive pattern 107 d is electrically connected to the conductivepattern 104 d through the contact hole, and the conductive pattern 107 eis electrically connected to the region of the semiconductor film 102 e,in which an impurity is introduced, through the contact hole. Theconductive pattern 107 d is an elongated rectangle and is locatedgenerally parallel to the auxiliary wiring 104 b. The conductive pattern107 e has a substantially frame shape and surrounds the conductivepattern 107 d.

The contact hole located above the conductive pattern 107 d is formed inthe second interlayer insulating film 106 b. The second electrode 108 iselectrically connected to the conductive patterns 107 d and 104 dthrough the contact hole.

The second auxiliary wiring 104 e is formed over the gate insulatingfilm 103. The second auxiliary wiring 104 e is located adjacent to theauxiliary wiring 104 b and extended parallel to the auxiliary wiring 104b. A plurality of contact holes located over the second auxiliary wiring104 e are formed in the first interlayer insulating film 106 a. Theconductive pattern 107 e is electrically connected to the secondauxiliary wiring 104 e through the contact hole.

The second auxiliary wiring 104 e is located in the same layer as theconductive pattern 104 d but is separated. In a region in which thesecond auxiliary wiring 104 e is separated, the conductive pattern 104 dis located. The separated portions of the second auxiliary wiring 104 eare electrically connected to each other through the conductive pattern107 e. In the case where an n-type impurity is introduced to thesemiconductor film 102 e the potential of the second auxiliary wiring104 e is lower than the lowest potential of the source wiring 107 a. Inthe case where a p-type impurity is introduced to the semiconductor film102 e, the potential of the second auxiliary wiring 104 e is higher thanthe highest potential of the source wiring 107 a.

In the liquid crystal display device with such a structure, when adriving thin film transistor is turned on, charge is accumulated in apart of the conductive pattern 104 e, which is located under theconductive pattern 104 d. The capacitor 118 functions in such a manner.

The semiconductor film 102 e is formed in the same step as thesemiconductor film 102 f. The conductive pattern 104 d and the secondauxiliary wiring 104 e are formed in the same step as the auxiliarywiring 104 b. In a step of forming the impurity regions 102 b and 102 dby injecting an impurity into the semiconductor film 102 f, the impurityis injected into a region in the semiconductor film 102 e which is notcovered with the conductive pattern 104 d. The conductive patterns 107 dand 107 e are formed in the same step as the source wiring 107 a. Inaddition, the contact holes formed in the first interlayer insulatingfilm 106 a are formed in the same step, and the contact holes formed inthe second interlayer insulating film 106 b are formed in the same step.Other steps of the manufacturing steps of the liquid crystal displaydevice are similar to those of the liquid crystal display deviceaccording to Embodiment Mode 3.

With this embodiment mode, an effect similar to Embodiment Mode 3 can beobtained. In addition, since the capacitor 118 is connected between thesecond electrode 108 functioning as the pixel electrode and the secondauxiliary wiring 104 e, the voltage of the second electrode 108 iseasily kept when the thin film transistor is turned off. In addition, inthe step of forming the impurity regions 102 b and 102 d by injecting animpurity into the semiconductor film 102 f, since the impurity isinjected into a region in the semiconductor film 102 e, which is notcovered with the conductive pattern 104 d and the impurity is notrequired to be injected into a region in the semiconductor film 102 e,which is covered with the conductive pattern 104 d; the number ofmanufacturing steps is not necessarily increased.

Note that the capacitor 118 may be provided in Embodiment Mode 1. Inthat case, an effect similar to this embodiment mode can be obtained.

In embodiment mode, the opening patterns 112 and 115 may have the shapeshown in FIGS. 10A and 10B, or 11A and 11B. Alternatively, the openingpattern 112 may have the shape shown in FIGS. 7A and 7B, or 9A and 9B.In this case, the opening pattern 115 has a shape of the opening pattern112 shown in FIGS. 7A and 7B, or 9A and 9B. Note that the openingpatterns 112 and 115 are required to be arranged so that the firstelectrode 102 c and the second electrode 108 are alternately arrangedand are generally in parallel except in the periphery portions, whenseen from the direction perpendicular to the substrate 100 of the liquidcrystal display device.

The impurity region 102 b functioning as a drain or a source of thetransistor is directly connected to the first electrode 102 c. In otherwords, the semiconductor layer in the transistor and the first electrode102 c are contiguous with each other to form one island. In addition,unlike Embodiment Mode 1, the contact hole located over the impurityregion 102 b and the contact hole located over the first electrode 102 care not formed in the first interlayer insulating film 106 a.Accordingly, the region for the contact holes can be utilized fordisplaying an image, which leads to improvement in aperture ratio.

If the opening patterns are thus provided to have differentorientations, a plurality of regions with different moving directions ofliquid crystal molecules can be provided. In other word, a multidomainstructure can be realized. When a multidomain structure is employed, itcan be prevented that an image cannot be displayed properly if seen froma certain direction. Accordingly, the viewing angle can be improved.

Note that the first electrode 102 c has the opening pattern 115 in thisembodiment mode. Therefore, in a portion of the opening pattern, theamount of light transmitted therethrough is increased. This is becausethe first electrode 102 is not provided in that portion. In a portionwhere the first electrode 102 is provided, the amount of lighttransmitted therethrough is decreased because the light transmittance isnot 100%. On the other hand, in a portion where the first electrode 102is not provided, light does not attenuate, which leads to increase inamount of light transmitted therethrough. As a result, it is possible toincrease luminance and to reduce power consumption.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 7 is partially changed, improved,or transformed. Therefore, the description in Embodiment Modes 1 to 7can be applied to or combined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 9

FIG. 16A is a circuit diagram of a liquid crystal display deviceaccording to Embodiment Mode 9. In the liquid crystal display deviceaccording to this embodiment mode, a plurality of pixels are arranged inmatrix. A structure of each pixel is similar to the structure of theliquid crystal display device according to Embodiment Mode 7, exceptthat a second auxiliary wiring 104 f extended in a longitudinaldirection is formed. The second auxiliary wiring 104 f is formed in thesame layer as the auxiliary wiring 104 b and is electrically connectedto the auxiliary wirings 104 b at each intersection with the auxiliarywirings 104 b.

According to this embodiment mode, an effect similar to Embodiment Mode7 can be obtained. Further, by provision of the second auxiliary wiring104 f, the potential of the common electrode can be easily held at thesame value in all pixels. Note that the liquid crystal display deviceaccording to this embodiment mode may be the FFS mode or the IPS mode.Although opening patterns included in the pixel electrode and the commonelectrode may have a shape similar to those shown in Embodiment Modes 1to 8, it is not limited thereto.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 8 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 8 can be applied to or combinedwith this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 10

FIG. 16B is a circuit diagram of a liquid crystal display deviceaccording to Embodiment Mode 10. In the liquid crystal display deviceaccording to this embodiment mode, a plurality of pixels are arranged inmatrix. A structure of each pixel is similar to the structure of theliquid crystal display device according to Embodiment Mode 8.

According to this embodiment mode, an effect similar to Embodiment Mode8 can be obtained. Note that the liquid crystal display device accordingto this embodiment mode may be the FFS mode or the IPS mode. Althoughopening patterns included in the pixel electrode and the commonelectrode may have a shape similar to those shown in Embodiment Modes 1to 8, it is not limited thereto.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 9 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 9 can be applied to or combinedwith this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 11

FIG. 17A is a circuit diagram of a liquid crystal display deviceaccording to Embodiment Mode 11. The liquid crystal display deviceaccording to this embodiment mode is the FFS mode or the IPS mode, andone pixel includes a plurality of (for example, two) subpixels. Astructure of each subpixel is similar to any of the structures of thepixel shown in Embodiment Modes 1 to 10. Therefore, the description inEmbodiment Modes 1 to 10 can be applied to this embodiment mode. FIG.17A shows an example where the pixel has a structure similar to thatshown in Embodiment Mode 7. Hereinafter, the component similar to thatof Embodiment Mode 7 is denoted by the same reference numeral anddescription thereof is omitted.

A plurality of subpixels forming one pixel are electrically connected tothe same gate wiring 104 c and are electrically connected to thedifferent auxiliary wirings 104 b from each other.

According to this embodiment mode, an effect similar to the liquidcrystal display device shown in Embodiment Modes 1 to 10 can beobtained. Furthermore, since one pixel includes a plurality ofsubpixels, a viewing angle can be further increased. Effects in whichthe pixel can have redundancy and area gray scale display can berealized can be obtained as well.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 10 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 10 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 12

FIG. 17B is a circuit diagram of a liquid crystal display deviceaccording to Embodiment Mode 12. The liquid crystal display deviceaccording to this embodiment mode is the FFS mode or the IPS mode. Astructure is similar to that of Embodiment Mode 11, except that aplurality of subpixels forming one pixel are electrically connected tothe different gate wirings 104 c from each other and are electricallyconnected to the same auxiliary wiring 104 b. A structure of each ofsubpixels is similar to any of the structures of the pixel shown inEmbodiment Modes 1 to 10. Therefore, the description in Embodiment Modes1 to 10 can be applied to this embodiment mode. FIG. 17B shows anexample where the pixel has a structure similar to that shown inEmbodiment Mode 7. Hereinafter, the component similar to that ofEmbodiment Mode 7 is denoted by the same reference numeral anddescription thereof is omitted. According to this embodiment mode, aneffect similar to Embodiment Mode 11 can be obtained.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 11 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 11 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 13

FIG. 18A is a plan view illustrating a structure of a liquid crystaldisplay device according to Embodiment Mode 13 in the present invention.FIG. 18B is a cross-sectional view along a line A-B and a line C-D ofFIG. 18A. A structure of this embodiment mode is similar to that ofEmbodiment Mode 1, except that a transistor for driving a pixel is abottom gate transistor and the base insulating film 101 is not formed.That is, the liquid crystal display device in this embodiment mode isthe FFS mode. Therefore, the description in Embodiment Mode 1 can beapplied to this embodiment mode. Hereinafter, the component similar tothat of Embodiment Mode 1 is denoted by the same reference numeral anddescription thereof is omitted.

In this embodiment mode, the gate electrode 104 a, the auxiliary wiring104 b, and the gate wiring 104 c are formed over the substrate 100. Thegate insulating film 103 is formed over the substrate 100, the gateelectrode 104 a, the auxiliary wiring 104 b, and the gate wiring 104 c.The semiconductor film 102 f and the first electrode 102 c are formedover the gate insulating film 103.

A manufacturing method of the liquid crystal display device according tothis embodiment mode is as follows. First, a conductive film is formedover the substrate 100 and is selectively etched. Therefore, the twogate electrodes 104 a, the auxiliary wiring 104 b, and the gate wiring104 c are formed over the substrate 100. Note that as the conductivefilm, a film formed of aluminum (Al), nickel (Ni), tungsten (W),molybdenum (Mo), titanium (Ti), tantalum (Ta), neodymium (Nd), platinum(Pt), gold (Au), silver (Ag), or the like; a film formed of an alloythereof; or a stacked-layer film thereof can be used. Alternatively,silicon (Si) in which an n-type impurity is introduced may be used.Next, the gate insulating film 103 is formed.

Next, a polysilicon film is formed over the gate insulating film 103,and a resist pattern is formed over the polysilicon film. Next, thepolysilicon film is etched with use of the resist pattern as a mask. Inthis manner, the semiconductor film 102 f and the first electrode 102 care formed in the same step. Thereafter, the resist pattern is removed.

Next, a mask pattern is formed over the semiconductor film 102 f, and animpurity is injected into the semiconductor film 102 f with use of themask pattern as a mask. Therefore, the impurity regions 102 b and 102 dand an impurity region between the gate electrodes 104 a are formed.Note that by this treatment, the impurity is also injected into thefirst electrode 102 c. In a case where the substrate 100 is formed usinga light-transmitting material such as glass, a mask may be formed bylight exposure from a rear face of the substrate 100 with use of thegate wiring as a light exposure pattern, without using a light exposuremask. In this case, the number of steps can be reduced since a lightexposure mask is not used, so that manufacturing cost can be reduced.Further, there is an advantage in that a mask pattern can be formed in aself-aligned manner, so that deviation of a mask pattern is reduced andthe deviation is not required to be considered. Subsequent steps aresimilar to those in Embodiment Mode 1.

According to this embodiment mode, an effect similar to Embodiment Mode1 can be obtained. Note that in the FFS mode liquid crystal displaydevice shown in Embodiment Mode 2 or 5, the transistor for driving apixel may be a bottom gate transistor having a structure similar to thisembodiment mode. Further, in the IPS mode liquid crystal display deviceshown in any one of Embodiment Modes 3, 4, and 6 to 12, the transistorfor driving a pixel may be a bottom gate transistor having a structuresimilar to this embodiment mode. In this manner, in any of theaforementioned FFS mode liquid crystal display devices and IPS modeliquid crystal display devices, the bottom gate transistor can beadopted.

In the liquid crystal display device according to this embodiment mode,or in the liquid crystal display device in any of Embodiment Modes 1 to12, of which transistor for driving the pixel is a bottom gatetransistor having a structure similar to this embodiment mode, the gateinsulating layer 103 over the substrate 100 may be removed except in aportion around the gate electrode 104 a before the polysilicon film isformed over the gate insulating layer 103. In this case, the firstelectrode 102 c is formed directly on the substrate 100.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 12 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 12 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 14

FIG. 19A is a cross-sectional view illustrating a structure of a liquidcrystal display device according to Embodiment Mode 14 in the presentinvention. The cross-sectional view corresponds to a cross section A-Band a cross section C-D of FIGS. 12A and 12B. A structure of thisembodiment mode is similar to that of the FFS mode liquid crystaldisplay device in Embodiment Mode 5, except that all parts of the secondelectrode 108 are provided over the first interlayer insulating film 106a and a part of the drain wiring 107 b is provided over the secondelectrode 108. In this embodiment mode, the drain wiring 107 b is formedafter the second electrode 108 is formed. Breakage of the secondelectrode 108 can be prevented by such a structure. That is, if thesecond electrode 108 is formed over the drain wiring 107 b as shown inEmbodiment Mode 5, the drain wiring 107 b is often made thicker than thesecond electrode 108, so that breakage of the second electrode 108 mightbe caused at an end portion of the drain wiring 107 b. On the otherhand, when the second electrode 108 is formed under the drain wiring 107b as shown in this embodiment mode, the breakage of the second electrode108 can be prevented. Note that since the drain wiring 107 b is oftenformed to be thick, breakage of the drain wiring 107 b is unlikely to becaused.

In addition, a manufacturing method of the liquid crystal display deviceaccording to this embodiment mode is generally similar to that ofEmbodiment Mode 5. Therefore, the description in Embodiment mode 5 canbe applied to this embodiment mode. Hereinafter, a component same asEmbodiment Mode 5 is denoted by the same reference numeral anddescription thereof is omitted. Note that although the opening pattern112 included in the second electrode 108 can have a shape shown in anyof Embodiment Modes 1 to 4 and 7, it is not limited thereto.

According to this embodiment mode, an effect similar to Embodiment Mode5 can be obtained. Note that an opening pattern parallel to the openingpattern 112 included in the second electrode 108 may be formed in thefirst electrode 102 c, so that the IPS mode liquid crystal displaydevice can be realized. The opening pattern can have a shape shown inany of Embodiment Modes 1 to 4 and 7. Note that the opening pattern inthe first electrode 102 c and the opening pattern 112 are required to bearranged so that the first electrode 102 c and the second electrode 108are alternately arranged and generally in parallel except in theperipheral portions when seen from the direction perpendicular to thesubstrate 100 of the liquid crystal display device.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 13 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 13 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 15

FIG. 19B is a cross-sectional view illustrating a structure of a liquidcrystal display device according to Embodiment Mode 15 in the presentinvention. The cross-sectional view corresponds to a cross section A-Band a cross section C-D of FIGS. 7A and 7B. A structure of thisembodiment mode is similar to that of the FFS mode liquid crystaldisplay device in Embodiment Mode 1, except that a second drain wiring116 is formed over the second interlayer insulating film 106 b and thesecond electrode 108 is formed so as to cover the second drain wiring116. Note that the second electrode 108 may partially overlap the seconddrain wiring 116. In addition, a manufacturing method of the liquidcrystal display device according to this embodiment mode is generallysimilar to that of Embodiment Mode 1. Therefore, the description inEmbodiment mode 1 can be applied to this embodiment mode. Hereinafter, acomponent same as Embodiment Mode 1 is denoted by the same referencenumeral and description thereof is omitted. Note that although theopening pattern 112 included in the second electrode 108 can have ashape shown in any of Embodiment Modes 1 to 4 and 7, it is not limitedthereto.

According to this embodiment mode, an effect similar to Embodiment Mode1 can be obtained. Note that the opening pattern parallel to the openingpattern 112 included in the second electrode 108 may be formed in thefirst electrode 102 c, so that the IPS mode liquid crystal displaydevice can be realized. The opening pattern can have a shape shown inany of Embodiment Modes 1 to 4 and 7. Note that the opening pattern inthe first electrode 102 c and the opening pattern 112 are required to bearranged so that the first electrode 102 c and the second electrode 108are alternately arranged and generally in parallel except in theperipheral portions when seen from the direction perpendicular to thesubstrate 100 of the liquid crystal display device.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 14 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 14 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 16

FIG. 20 is a cross-sectional view illustrating a structure of a pixelportion in an FFS mode liquid crystal display device according toEmbodiment Mode 16 in the present invention. A structure of the pixelportion of the liquid crystal display device according to thisembodiment mode is generally similar to that of the liquid crystaldisplay device in Embodiment Mode 1, except that a red color filter 130r, a green color filter 130 g, and a blue color filter 130 b areprovided instead of the first interlayer insulating film 106 a.Therefore, the description in Embodiment mode 1 can be applied to thisembodiment mode. Hereinafter, the component similar to that ofEmbodiment Mode 1 is denoted by the same reference numeral anddescription thereof is omitted. Note that since the insulating film 105is provided between the semiconductor film 102 f and the color filters130 r, 130 g, and 130 b, it also functions to suppress diffusion ofimpurities from each color filter to the semiconductor film 102 f.

A manufacturing method of the liquid crystal display device according tothis embodiment mode is similar to that of Embodiment Mode 1, exceptthat a step of forming the color filters 130 r, 130 g, and 130 b isadded instead of a step of forming the first interlayer insulating film106 a. The color filters 130 r, 130 g, and 130 b are formed by repeatingthe following steps three times: a step of forming a color filter layer,a step of forming a resist pattern over the color filter layer, and astep of selectively dry-etching the color filter layer with use of theresist pattern as a mask. Note that the second interlayer insulatingfilm 106 b is embedded in a space which is generated between colorfilters. Alternatively, the color filters 130 r, 130 g, and 130 b can beformed by using a droplet discharging method (such as an ink-jetmethod).

Accordingly, the number of manufacturing steps can be reduced. Further,since the color filter is provided on the substrate 100 side, reductionin an aperture ratio can be suppressed even when misalignment with theopposite substrate is caused, as compared with a case where a colorfilter is provided on the opposite substrate side. That is, a margin forthe misalignment of the opposite substrate is increased.

Note that colors of the color filter may be a color other than red,blue, and green; or may be more than three colors, for example, fourcolors or six colors. For example, yellow, cyan, magenta, or white maybe added. Further, a black matrix (also called a black mask) may beprovided in addition to the color filters.

FIG. 21A is a plan view of the liquid crystal display device shown inFIG. 20. As shown in FIG. 21A, in the liquid crystal display device, asource line driver circuit 160 and a gate line driver circuit 170, whichare peripheral driver circuits, are provided in the periphery of a pixelportion 150. The red color filter 130 r is provided over each of thesource line driver circuit 160 and the gate line driver circuit 170. Byprovision of the red color filter 130 r, light degradation of an activelayer in a thin film transistor included in the source line drivercircuit 160 and the gate line driver circuit 170 is prevented, andplanarization is realized.

FIG. 21B is an enlarged view of a part of the pixel portion 150 (threerows×three columns) in FIG. 21A. In the pixel portion 150, the red colorfilter 130 r, the blue color filter 130 b, and the green color filter130 g are alternately arranged in stripes. Further, the red color filter130 r is provided over a thin film transistor included in each pixel.

Since a source wiring (not shown) and a gate wiring (not shown) arearranged so as to overlap with the space between each color filter,light leakage is suppressed.

Since the color filter 130 r functions as a black mask in this manner, astep of forming a black mask, which is conventionally required, can beomitted.

As described above, according to this embodiment mode, an effect similarto Embodiment Mode 1 can be obtained. Further, since the color filters130 r, 130 b, and 130 g are provided instead of the first interlayerinsulating film 106 a, the number of manufacturing steps of the liquidcrystal display device can be reduced. Moreover, reduction in anaperture ratio can be suppressed even when misalignment with theopposite substrate is caused, as compared with a case where the colorfilter is provided on the opposite substrate side. That is, a margin forthe misalignment of the opposite substrate is increased.

Note that in the FFS mode or the IPS mode liquid crystal display devicesshown in Embodiment Modes 2 to 4, 6 to 13, and 15, the color filters 130r, 130 b, and 130 g may be provided instead of the first interlayerinsulating film 106 a similar to this embodiment mode. In this case, aneffect similar to this embodiment mode can be obtained.

Note that although a color filter may be provided between the gateelectrode and the source wiring, it is not limited thereto. The colorfilter may be provided between the source wiring and the secondelectrode 108.

Further, a black matrix may be provided in addition to a color filter.

Note that an insulating film of an inorganic material may be providedbetween the color filter and the source wiring, or between the colorfilter and the second electrode 108. The inorganic material is formed ofan insulating substance containing oxygen or nitride, such as siliconoxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y): x>y), or silicon nitride oxide (SiN_(x)O_(y): x>y). Inorder to block intrusion of impurities, a material containing a largeamount of nitrogen is preferably employed.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 15 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 15 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 17

FIG. 22A is a plan view illustrating a structure of an FFS mode liquidcrystal display device according to Embodiment Mode 17 in the presentinvention. FIG. 22B is an enlarged view illustrating a structure of apixel portion in FIG. 22A. A structure of the liquid crystal displaydevice according to this embodiment mode is similar to that ofEmbodiment Mode 16, except for the layout of the color filters 130 r,130 b, and 130 g. Therefore, the description in Embodiment mode 16 canbe applied to this embodiment mode. Hereinafter, the component similarto that of Embodiment Mode 16 is denoted by the same reference numeraland description thereof is omitted.

In this embodiment mode, the pixels provided with the color filter 130r, 130 b, or 130 g are arranged in matrix so that the color filters 130r, 130 b, and 130 g are alternately arranged. Specifically, the redcolor filter 130 r is provided so as to fill a gap between the bluecolor filter 130 b and the green color filter 130 g. Further, the redcolor filter 130 r is also provided over the source line driver circuit160 and the gate line driver circuit 170, which are peripheral drivercircuits; and provided in spaces between the pixel portion 150 and eachof the source line driver circuit 160 and the gate line driver circuit170. Therefore, generation of a space between color filters issuppressed.

According to this embodiment mode, an effect similar to Embodiment Mode16 can be obtained. Note that after the first interlayer insulating film106 a is formed, the color filters 130 r, 130 b, and 130 g may beprovided instead of the second interlayer insulating film 106 b. In thiscase, an effect similar to this embodiment mode can be obtained.

Note that in the FFS mode or the IPS mode liquid crystal display devicesshown in Embodiment Modes 2 to 4, 6 to 13, and 15, the color filters 130r, 130 b, and 130 g may be provided instead of the first interlayerinsulating film 106 a similar to this embodiment mode. In this case, aneffect similar to this embodiment mode can be obtained.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 16 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 16 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 18

FIG. 23 is a cross-sectional view illustrating a structure of an FFSmode liquid crystal display device according to Embodiment Mode 18 inthe present invention. A structure of the liquid crystal display deviceaccording to this embodiment mode is similar to that in Embodiment Mode5, except that the color filters 130 r, 130 b, and 130 g are providedinstead of the first interlayer insulating film 106 a. The layout of thecolor filters 130 r, 130 b, and 130 g in this embodiment mode is similarto that of Embodiment Mode 17. Therefore, the description in Embodimentmodes 5 and 17 can be applied to this embodiment mode. Hereinafter, thecomponent similar to that of Embodiment Modes 5 and 17 is denoted by thesame reference numeral and description thereof is omitted.

According to this embodiment mode, an effect similar to Embodiment Mode17 can be obtained. Note that in the FFS mode liquid crystal displaydevices shown in Embodiment Mode 14, the color filters 130 r, 130 b, and130 g may be provided instead of the first interlayer insulating film106 a similar to this embodiment mode. In this case, an effect similarto this embodiment mode can be obtained.

Note that the layout of the color filters 130 r, 130 b, and 130 g is notlimited to those shown in Embodiment Modes 16 to 18, and various layoutssuch as a triangle mosaic arrangement, an RGBG four pixel arrangement,or an RGBW four pixel arrangement may be employed. In these cases, thered color filter 130 r is preferably provided above an active layer of athin film transistor.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 17 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 17 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 19

Each of FIGS. 24A to 24D is a plan view illustrating a structure of anelectrode of an FFS mode liquid crystal display device according toEmbodiment Mode 19 in the present invention. Since a structure shown ineach drawing is similar to the FFS mode liquid crystal display deviceaccording to Embodiment Mode 1, except for a shape of the secondelectrode 108, components other than the first electrode 102 c and thesecond electrode 108 are not shown in the drawing.

In FIG. 24A, the second electrode 108 has a comb shape. A space betweeneach comb-tooth functions as the opening pattern 112 shown in EmbodimentMode 1.

In FIG. 24B, the second electrode 108 has a shape in which a pluralityof electrodes each having a shape along a circumference of a circle, ofwhich radius is different from each other, are arranged in a concentricpattern and is connected to each other. A space between each electrodefunctions as the opening pattern 112 shown in Embodiment Mode 1.

In FIG. 24C, the second electrode 108 has a shape in which a pluralityof linear electrodes extended in a long side direction of therectangular first electrode 102 c are arranged over the first electrode102 c so as not to overlap with each other; and each of the linearelectrodes has its upper portion connected to an upper portion of anadjacent linear electrode and its lower end portion connected to anlower end portion of the other adjacent linear electrode. That is, thesecond electrode 108 has a shape in which an elongated electrode is ledup and down repeatedly over the first electrode 102 c, and its one endportion is arranged nearest to one long side of the first electrode 102c (in FIG. 24C, a long side on the right side) and is connected nowhere.Further, a space between each linear electrode functions as the openingpattern 112 shown in Embodiment Mode 1.

In FIG. 24D, the second electrode 108 has a shape in which in the secondelectrode 108 shown in FIG. 24C, the end portion nearest to one longside of the first electrode 102 c (in FIG. 24C, the long side on theright side) is further extended and led along a short side of the firstelectrode 102 c (in FIG. 24D, a short side on the upper side), andconnected to a portion nearest to the other long side of the firstelectrode 102 c (in FIG. 24C, the long side on the left side). Sinceboth the end portions of the second electrode 108 are connected to eachother, a potential of the second electrode 108 can be easily keptconstant as compared with the shape shown in FIG. 24C.

A manufacturing method of the liquid crystal display device according tothis embodiment mode is generally similar to that of Embodiment Mode 1in each case. Therefore, the description in Embodiment mode 1 can beapplied to this embodiment mode.

According to this embodiment mode, an effect similar to Embodiment Mode1 can be obtained. Note that in Embodiment Modes 2, 5, and 13 to 18, thesecond electrode 108 may have a shape shown in any of FIGS. 24A to 24D.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 18 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 18 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 20

Each of FIGS. 25A to 25D is a plan view illustrating a structure of anelectrode of an IPS mode liquid crystal display device according toEmbodiment Mode 20 in the present invention. Since a structure of thisembodiment mode is similar to that of Embodiment Mode 3, except for theshape of the first electrode 102 c and the second electrode 108,components other than the first electrode 102 c and the second electrode108 are not shown in the drawing.

In FIG. 25A, each of the first electrode 102 c and the second electrode108 has a comb shape, and is arranged to face opposite directions fromeach other. Comb-teeth are alternately arranged.

In FIG. 25B, the first electrode 102 c has a shape in which the circularopening pattern 115 is provided at the center of its rectangular body;and in the opening pattern 115, a plurality of electrodes each having ashape along a circumference of a circle, of which radius are differentfrom each other, are arranged concentrically with the opening pattern115 and each electrode having a shape along the circumference of thecircle is connected to the body by one linear electrode. The secondelectrode 108 has a shape in which the circular opening pattern 112 isprovided at the center of the rectangular body; and in the openingpattern 112, an electrode having a shape along the circumference of thecircle is arranged concentrically with the opening pattern 112 and theelectrode and the body are connected by a linear electrode. Note thatthe electrode having a shape along the circumference of the circleincluded in the second electrode 108 may be plural.

Since the opening patterns 112 and 115 are concentric with each other,the electrode having a shape along the circumference of the circleincluded in the first electrode 102 c and the electrode having a shapealong the circumference of the circle included in the second electrode108 are concentric with each other. Note that the electrode having ashape along the circumference of the circle included in the firstelectrode 102 c and the electrode having a shape along the circumferenceof the circle included in the second electrode 108 have differentradiuses from each other, so that they are alternately arranged inparallel with each other.

In FIG. 25C, the first electrode 102 c has a shape in which a pluralityof linear electrodes extended up and down in the drawing are arranged inparallel with each other and each of upper end portions or lower endportions thereof is connected by a linear electrode extended in thelateral direction in the drawing. The second electrode 108 has a combshape, and comb-teeth are provided in a space between the linearelectrodes forming the first electrode 102 c.

In FIG. 25D, the first electrode 102 c and the second electrode 108 havea shape in which a plurality of linear electrodes extended up and downin the drawing are arranged in parallel with each other so as not tooverlap with each other; and each of the linear electrodes has its upperportion connected to an upper portion of an adjacent linear electrodeand its lower end portion connected to an lower end portion of the otheradjacent linear electrode. That is, the second electrode 108 has a shapein which an elongated electrode is led up and down repeatedly over thefirst electrode 102 c. Further, in the first electrode 102 c and thesecond electrode 108, portions extended up and down in the drawing arealternately arranged in parallel with each other, and portions extendedin the lateral direction do not overlap with each other.

A manufacturing method of the liquid crystal display device according tothis embodiment mode is generally similar to that of Embodiment Mode 3in each case. Therefore, the description in Embodiment mode 3 can beapplied to this embodiment mode.

According to this embodiment mode, an effect similar to Embodiment Mode3 can be obtained. Note that in Embodiment Modes 4, and 6 to 12, thefirst electrode 102 c and the second electrode 108 may have a shapeshown in any of FIGS. 25A to 25D.

In addition, in each embodiment mode described above, anothersemiconductor film (for example, an organic semiconductor film or anamorphous silicon film) may be used instead of the semiconductor film102 f. In this case, the first electrode 102 c may also be formed of theaforementioned another semiconductor film.

Note that this embodiment mode shows an example in a case where thedescription in Embodiment Modes 1 to 19 is partially changed, improved,transformed, or is described from a different perspective. Therefore,the description in Embodiment Modes 1 to 19 can be applied to orcombined with this embodiment mode.

In addition, description is made with reference to various drawings. Onedrawing includes various components. Therefore, another structure can bemade by combining components selected from different drawings.

Embodiment Mode 21

FIGS. 32A and 32B are cross-sectional views illustrating a structure ofan inorganic EL element using the present invention. The inorganic ELelement according to the present invention has a structure using abottom gate transistor, and the structure is similar to the liquidcrystal display device according to Embodiment Mode 13 in that the firstelectrode 102 c and the second electrode 108 are used. A structure of atransistor, an electrode, or the like is not limited to that shown inthis embodiment mode; and a top gate transistor or a structure of anelectrode shown in another embodiment mode may be used. Although onlyone transistor is shown in the cross-sectional views shown in thisembodiment mode, a structure where a plurality of transistors, such as adriving transistor, a selection transistor, or a transistor forcontrolling current, are included in one pixel may be employed. As amaterial to be used for the second electrode, one or more elementsselected from aluminum (Al), tantalum (Ta), titanium (Ti), molybdenum(Mo), tungsten (W), neodymium (Nd), chromium (Cr), nickel (Ni), platinum(Pt), gold (Au), silver (Ag), copper (Cu), magnesium (Mg), scandium(Sc), cobalt (Co), zinc (Zn), niobium (Nb), silicon (Si), phosphorus(P), boron (B), arsenic (As), gallium (Ga), indium (In), and tin (Sn); acompound or an alloy material containing one or more of theaforementioned elements (such as indium tin oxide (ITO), indium zincoxide (IZO), indium tin oxide doped with silicon oxide (ITSO), zincoxide (ZnO), aluminum neodymium (Al—Nd), or magnesium silver (Mg—Ag)); asubstance obtained by combining such compounds; or the like may beemployed. Alternatively, a compound (silicide) of silicon and theaforementioned material (such as aluminum silicon, molybdenum silicon,or nickel silicide) or a compound of nitride and the aforementionedmaterial (such as titanium nitride, tantalum nitride, or molybdenumnitride) can be used. Note that silicon (Si) may contain a large amountof n-type impurities (phosphorus or the like) or p-type impurities(boron or the like).

Inorganic EL elements are classified into a dispersion-type inorganic ELelement and a thin-film type inorganic EL element, according to thestructure of the element. These differ in that the former includes alayer including a light emitting material, in which particles of thelight emitting material are dispersed in a binder, and the latterincludes a layer including a light emitting material formed as a thinfilm. However, the dispersion-type inorganic EL element and thethin-film type inorganic EL element are common in that electronsaccelerated by a high electric field are required. In this embodimentmode, a layer 501 including a light emitting material is provided abovethe second electrode 108. In a case of a dispersion-type inorganic ELelement, a structure where the layer 501 including the light emittingmaterial is provided on and in contact with the second electrode 108(see FIG. 32A) is preferably employed; however, it is not limitedthereto. In a case of a thin-film type inorganic EL element, a structurewhere a dielectric 502 is formed over the second electrode 108 and thelayer 501 including the light emitting material is provided over thedielectric 502 (see FIG. 32B) is preferably employed; however, it is notlimited thereto.

As a mechanism of light emission, donor-acceptor recombination emissionin which a donor level and an acceptor level are utilized, and localemission in which inner shell electron transition in a metal ion isutilized are known. Generally, the dispersion-type inorganic EL elementtypically employs donor-acceptor recombination emission and thethin-film type inorganic EL element typically employs local emission.

The layer 501 including the light emitting material includes a basematerial and an impurity element to be a luminescent center. By changeof the impurity element to be included, various colors of light emissioncan be obtained. As a manufacturing method of the light emittingmaterial, a spraying thermal decomposition method, a doubledecomposition method, a method by thermal decomposition reaction of aprecursor, a reversed micelle method, a method in which these methodsand high temperature firing are combined, a freeze-drying method, or thelike can be used.

The solid phase method is a method in which a compound including a basematerial and an impurity element or a compound including the impurityelement are weighed, mixed in a mortar, heated in an electric-furnace,and baked to react so that the impurity element is included in the basematerial. The baking temperature is preferably 700 to 1500° C. This isbecause solid-phase reaction does not proceed when the temperature istoo low, and the base material is decomposed when the temperature is toohigh. Note that although baking may be performed in a powder state, itis preferably performed in a pellet state. It is suitable formass-production since it is a simple method with high productivity eventhough baking at a comparatively high temperature is required.

The liquid phase method (the coprecipitation method) is a method inwhich a base material or a compound including the base material, and animpurity element or a compound including the impurity element arereacted in a solution, dried, and then baked. The particles of the lightemitting material are dispersed uniformly, and the reaction can beadvanced even if the particles are small and baking temperature is low.

As the base material to be used for the light emitting material, asulfide, an oxide, or a nitride can be used. As a sulfide, zinc sulfide(ZnS), cadmium sulfide (CdS), calcium sulfide (CaS), yttrium sulfide(Y₂S₃), gallium sulfide (Ga₂S₃), strontium sulfide (SrS), barium sulfide(BaS), or the like can be used, for example. As an oxide, zinc oxide(ZnO), yttrium oxide (Y₂O₃), or the like can be used, for example.

In addition, as a nitride, aluminum nitride (AlN), gallium nitride(GaN), indium nitride (InN), or the like can be used, for example.Alternatively, zinc selenide (ZnSe), zinc telluride (ZnTe), or the like;or a ternary mixed crystal such as calcium sulfide-gallium (CaGa₂S₄),strontium sulfide-gallium (SrGa₂S₄), or barium sulfide-gallium (BaGa₂S₄)may be used.

As a luminescent center of local emission, manganese (Mn), copper (Cu),samarium (Sm), terbium (Tb), erbium (Er), thulium (Tm), europium (Eu),cerium (Ce), praseodymium (Pr), or the like can be used. For chargecompensation, a halogen element such as fluorine (F) or chlorine (Cl)may be added.

On the other hand, as a luminescent center of donor-acceptorrecombination emission, a light emitting material including a firstimpurity element forming a donor level and a second impurity elementforming an acceptor level can be used. As the first impurity element,fluorine (F), chlorine (Cl), aluminum (Al), or the like can be used, forexample. As the second impurity element, copper (Cu), silver (Ag), orthe like can be used, for example.

Note that in the inorganic EL light emitting element, a voltage isapplied between a pair of electrodes so that light emission can beobtained. In this embodiment mode, AC drive is preferably used since anelectric field formed by the first electrode 102 c and the secondelectrode 108 is used for light emission in the inorganic EL lightemitting element shown in this embodiment mode. Note that the electricfield formed for light emission is similar to the electric field in theliquid crystal display device shown in other embodiment modes.

As a binder which can be used in this embodiment mode, an organic orinorganic insulating material, or a mixed material of an organicmaterial and an inorganic material can be used. As the organicinsulating material, the following resin can be used: a polymer having acomparatively high dielectric constant such as a cyanoethyl cellulosebased resin; or a resin such as polyethylene, polypropylene, apolystyrene based resin, a silicone resin, an epoxy resin, or vinylidenefluoride. Further, a heat-resistant high-molecular material such asaromatic polyamide or polybenzimidazole, or a siloxane resin may also beused.

Alternatively, the following resin material may also be used: a vinylresin such as polyvinyl alcohol or polyvinylbutyral, a phenol resin, anovolac resin, an acrylic resin, a melamine resin, a urethane resin, anoxazole resin (polybenzoxazole), or the like. Further, a photo-curableresin or the like can be used. Fine particles having a high dielectricconstant such as barium titanate (BaTiO₃) or strontium titanate (SrTiO₂)may be mixed to these resins as appropriate, so that a dielectricconstant can be adjusted.

As the inorganic material used for the binder, silicon oxide (SiO_(x)),silicone nitride (SiN_(x)), silicon containing oxygen and nitrogen,aluminum nitride (AlN), aluminum containing oxygen and nitrogen,aluminum oxide (Al₂O₃), titanium oxide (TiO₂), BaTiO₃, SrTiO₃, leadtitanate (PbTiO₃), potassium niobate (KNbO₃), lead niobate (PbNbO₃),tantalum oxide (Ta₂O₅), barium tantalate (BaTa₂O₆), lithium tantalate(LiTaO₃), yttrium oxide (Y₂O₃), zirconium oxide (ZrO₂), ZnS, or amaterial selected from a substance including other inorganic materialscan be employed. By adding the inorganic material having a highdielectric constant in the organic material (by doping or the like), thedielectric constant of a layer including a light emitting substanceformed of the light emitting material and the binder can be controlled,and the dielectric constant can be further increased.

As shown in this embodiment mode, an electrode containing silicon isused as an electrode of the inorganic EL element, so that the inorganicEL element can be manufactured at low cost. By the structure shown inthis embodiment mode, various electrode materials can be applied sinceattenuation by the electrode is not required to be considered. Forexample, the second electrode may be formed using a metal material so asto be thick. Further, since a layer including a light emitting materialis not required to be provided between the first electrode and thesecond electrode, luminance as a display device can be improved; a loadfor the EL element can be reduced; and deterioration of the element canbe reduced.

Embodiment Mode 22

FIG. 33 is a cross-sectional view illustrating a structure of an organicEL element which uses an electrode containing silicon in the presentinvention. The organic EL element according to this embodiment mode hasa structure where a bottom gate transistor 600 is used. In thisembodiment mode, a layer 601 including an organic compound is interposedbetween the first electrode 102 c and a second electrode 602. Astructure of a transistor is not limited to that shown in thisembodiment mode, and a top gate transistor may be used. As a materialused for the second electrode, one or more elements selected fromaluminum (Al), tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), neodymium (Nd), chromium (Cr), nickel (Ni), platinum (Pt), gold(Au), silver (Ag), copper (Cu), magnesium (Mg), scandium (Sc), cobalt(Co), zinc (Zn), niobium (Nb), silicon (Si), phosphorus (P), boron (B),arsenic (As), gallium (Ga), indium (In), tin (Sn), and oxygen (O); acompound or an alloy material containing one or more of theaforementioned elements (such as indium tin oxide (ITO), indium zincoxide (IZO), indium tin oxide doped with silicon oxide (ITSO), zincoxide (ZnO), aluminum neodymium (Al—Nd), or magnesium silver (Mg—Ag)); asubstance obtained by combining such compounds; or the like may beemployed. Alternatively, a compound (silicide) of silicon and theaforementioned material (such as aluminum silicon, molybdenum silicon,or nickel silicide) or a compound of nitride and the aforementionedmaterial (such as titanium nitride, tantalum nitride, or molybdenumnitride) can be used. Note that silicon (Si) may contain a large amountof n-type impurities (phosphorus or the like) or p-type impurities(boron or the like).

The layer 601 including the organic compound includes at least a layer(light emitting layer) including a material with a high light emittingproperty. There is no particular limitation on the light emitting layer;however, a layer functioning as the light emitting layer has roughly twomodes. One is a host-guest type layer which includes a light emittingsubstance dispersed in a layer formed of a material (host material)having an energy gap larger than an energy gap of a substance (lightemitting substance or guest material) to be a luminescent center. Theother is a layer in which a light emitting layer includes only a lightemitting material. The former is preferable since concentrationquenching hardly occurs. As the light emitting substance, the followingcan be employed:4-dicyanomethylene-2-methyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(abbreviation: DOT);4-dicyanomethylene-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran;periflanthene;2,5-dicyano-1,4-bis[2-(10-methoxy-1,1,7,7-tetramethyljulolidyl-9-enyl)]benzene;N,N′-dimethylquinacridone (abbreviation: DMQd); coumarin 6; coumarin545T; tris(8-quinolinolato)aluminum (abbreviation: Alq₃);9,9′-bianthryl; 9,10-diphenylanthracene (abbreviation: DPA);9,10-bis(2-naphthyl)anthracene (abbreviation: DNA);2,5,8,11-tetra-t-butylperylene (abbreviation: TBP); or the like. As thehost material, the following can be used: an anthracene derivative suchas 9,10-di(2-naphthyl)-2-tert-butylanthracene (abbreviation: t-BuDNA); acarbazole derivative such as 4,4′-bis(N-carbazolyl)biphenyl(abbreviation: CBP); or a metal complex such astris(8-quinolinolato)aluminum (abbreviation: Alq₃),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃);bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂);bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (abbreviation:BAlq); bis[2-(2-hydroxyphenyl)pyridinato]zinc (abbreviation: Znpp₂); orbis[2-(2-hydroxyphenyl)benzoxazolate]zinc (abbreviation: ZnBOX). As amaterial which is a light transmitting substance capable of forming thelight emitting layer alone, tris(8-quinolinolato)aluminum (abbreviation:Alq₃), 9,10-bis(2-naphthyl)anthracene (abbreviation: DNA),bis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (abbreviation:BAlq), or the like can be used. Note that as a layer including anorganic compound, a layer such as a hole injecting layer, a holetransporting layer, an electron transporting layer, or an electroninjecting layer may be included.

Note that an organic EL light emitting element can obtain light emissionwhen a voltage is applied between a pair of electrodes. In the organicEL light emitting element shown in this embodiment mode, light isemitted by a current generated by the first electrode 102 c and thesecond electrode 602.

As shown in this embodiment mode, the electrode containing silicon isused as an electrode of the organic EL element, so that the organic ELelement can be manufactured at low cost.

Embodiment Mode 23

FIGS. 34A to 34D are cross-sectional views illustrating a reflectiontype liquid crystal display device using a single crystalline siliconsubstrate, and a manufacturing method thereof. Hereinafter, themanufacturing method is briefly described. First, oxygen ions areimplanted into a single crystalline silicon substrate 700 with constantacceleration (see FIG. 34A). Thereafter, by heating at a hightemperature, a silicon oxide layer 702 is formed, while a singlecrystalline silicon layer 701 remains on a surface of the singlecrystalline silicon substrate 700 (see FIG. 34B). Next, the singlecrystalline silicon layer 701 is etched into an island shape so as toform a transistor 703. In this case, the first electrode 102 c is formedat the same time (see FIG. 34C). Note that an impurity element is addedto source and drain regions 704 of the transistor 703 so as to haveconductivity. As the impurity element, elements shown in otherembodiment modes can be used. Further, an electrode, a wiring, or thelike can be formed using a material shown in other embodiment modes.

Next, an interlayer insulating film 705 is formed (see FIG. 34C). Sincethe interlayer insulating film can be formed using a material shown inother embodiment modes and embodiments, detailed description is omittedhere. Note that in this embodiment mode, although the interlayerinsulating film has a single-layer structure, it may have astacked-layer structure of two or more layers. After the interlayerinsulating film 705 is formed, a contact hole is formed and a secondelectrode 706 to be a pixel electrode is formed (see FIG. 34D). In thisembodiment mode, as a material for the second electrode 706, a materialhaving high visible light reflectivity is preferably used since areflection type liquid crystal display device is formed; it is notlimited thereto. As a material having high reflectivity, a metalmaterial such as aluminum (Al), tantalum (Ta), titanium (Ti), molybdenum(Mo), tungsten (W), neodymium (Nd), chromium (Cr), nickel (Ni), platinum(Pt), gold (Au), silver (Ag), copper (Cu), magnesium (Mg), scandium(Sc), cobalt (Co), zinc (Zn), niobium (Nb), silicon (Si), phosphorus(P), boron (B), arsenic (As), gallium (Ga), indium (In), or tin (Sn) canbe taken as an example. Note that a wiring 707 for connection ispreferably formed at the same time as the electrode 706.

Thereafter, an alignment film, a liquid crystal, an opposite substrate,and the like are provided so that the reflection type liquid crystaldisplay device is completed. In the liquid crystal display device inthis embodiment mode, light from an upper surface (on an oppositesubstrate side) is reflected by the first electrode 102 c or the secondelectrode 706 so that an image is seen. Therefore, a material havinghigh reflectivity is preferably used for the second electrode 706.Crystal silicon which is a material of the first electrode 102 c has,depending on a state of a surface thereof, reflectivity higher than acertain value; therefore, it can be used as a reflective film of thereflection type liquid crystal display device. Note that a structure ofa reflection type liquid crystal display device is not limited to thatof this embodiment mode, and various structures can be used. Forexample, in this embodiment mode, a top gate transistor is used as thetransistor 703; however, a bottom gate transistor may be used. Further,an electrode formed of a metal material may be employed as the firstelectrode 102 c.

As shown in this embodiment mode, by use of a single crystalline siliconsubstrate, a liquid crystal display device suitable for usage requiringhigh-speed operation can be manufactured. That is, a driver circuit canbe manufactured directly on a substrate, and high-speed operation of thedriver circuit and the like can be achieved. Needless to say, not onlythe driver circuit but also other circuits can be formed using singlecrystalline silicon, so that a display device in which all circuits aremounted on one substrate can be formed.

Embodiment 1

Embodiment 1 of the present invention is described with reference toFIGS. 26A to 28B. In a liquid crystal display module according to thisembodiment, a pixel portion has a structure similar to that of theliquid crystal display device shown in any of Embodiment Modes 1 to 20.Therefore, manufacturing cost can be lowered as compared with aconventional device.

First, as shown in FIG. 26A, a base film 802 is formed over a substrate801. The substrate 801 is a glass substrate, a quartz substrate, asubstrate formed of an insulator such as alumina, a plastic substratewith enough heat resistance to withstand a processing temperature ofsubsequent steps, a silicon substrate, or a metal plate. Further, thesubstrate 801 may be a substrate in which an insulating film of siliconoxide, silicon nitride, or the like is formed over a surface of a metalsubstrate such as a stainless steel substrate or a surface of asemiconductor substrate. Note that when a plastic substrate is used forthe substrate 801, plastic with a comparatively high glass transitionpoint, such as PC (polycarbonate), PES (polyethersulfone), PET(polyethylene terephthalate), or PEN (polyethylene naphthalate) ispreferably used.

The base film 802 has a stacked-layer structure where a silicon oxide(SiO_(x)) film is formed over a silicon nitride (SiN_(x)) film, forexample; other insulators (such as silicon oxynitride (SiO_(x)N_(y))(x>y>0) or silicon nitride oxide (SiN_(x)O_(y)) (x>y>0)) may also beused. Alternatively, the base film 802 may be formed by high-densityplasma treatment on a surface of the substrate 801. High-density plasmais generated by using a microwave at, for example, 2.45 GHz, and haselectron density of 1×10¹¹ to 1×10¹³/cm³, electron temperature of 2 eVor less, and ion energy of 5 eV or less. Such high-density plasma haslow kinetic energy of active species, and a film with less plasma damageand fewer defects compared with conventional plasma treatment can beformed. The distance between the substrate 801 and an antenna forgenerating the microwave is set to 20 to 80 mm, preferably 20 to 60 mm.

The surface of the substrate 801 can be nitrided by performing theaforementioned high-density plasma treatment in a nitrogen atmosphere,for example, in an atmosphere including nitrogen and a rare gas, anatmosphere including nitrogen, hydrogen, and a rare gas, or anatmosphere including ammonia and a rare gas. When a glass substrate, aquartz substrate, a silicon wafer, or the like is used as the substrate801 and nitriding treatment is performed by the aforementionedhigh-density plasma, a nitride film formed on the surface of thesubstrate 801 contains silicon nitride as its main component, so thatthe nitride film can be used as the base film 802. A silicon oxide filmor a silicon oxynitride film may be formed over the nitride film by aplasma CVD method so that the base film 802 includes a plurality oflayers.

In addition, a nitride film can be formed on a surface of the base film802 including a silicon oxide film, a silicon oxynitride film, or thelike by similarly performing nitriding treatment with high-densityplasma on the surface of the base film 802. The nitride film cansuppress diffusion of impurities from the substrate 801 and can beformed to be very thin; therefore, influence of stress upon asemiconductor layer to be formed thereover can be reduced.

Next, as shown in FIG. 26B, a crystalline semiconductor film (such as apolysilicon film) is formed over the base film 802. As a forming methodof the crystalline semiconductor film, a method in which the crystallinesemiconductor film is formed directly on the base film 802, and a methodin which an amorphous semiconductor film is formed over the base film802 and subsequently crystallized can be taken as an example.

As a method of crystallizing the amorphous semiconductor film, thefollowing can be used: a crystallization method by laser lightirradiation; a crystallization method by heating using an element (forexample, a metal element such as nickel) which promotes crystallizationof the semiconductor film; or a crystallization method by heating usingan element which promotes crystallization of the semiconductor film andsubsequently irradiating the semiconductor film with laser light.Needless to say, a method of thermally crystallizing the amorphoussemiconductor film without using the aforementioned element can be usedas well. However, in this case, the substrate is required to be a quartzsubstrate, a silicon wafer, or the like which can withstand the hightemperature.

When laser irradiation is used, a continuous wave laser beam (CW laserbeam) or a pulsed laser beam (pulse laser beam) can be used. Here, alaser beam emitted from one or plural kinds of a gas laser such as an Arlaser, a Kr laser, or an excimer laser; a laser using, as a medium,single crystalline YAG, YVO₄, forsterite (Mg₂SiO₄), YAlO₃, or GdVO₄, orpolycrystalline (ceramic) YAG, Y₂O₃, YVO₄, YAlO₃, or GdVO₄ doped withone or more of Nd, Yb, Cr, Ti, Ho, Er, Tm, and Ta as a dopant; a glasslaser; a ruby laser; an alexandrite laser; a Ti:sapphire laser; a coppervapor laser; and a gold vapor laser can be used. By irradiation with alaser beam having a fundamental wave of such laser beams or one of thesecond to fourth harmonics of the fundamental wave, a crystal with alarge grain size can be obtained. For example, the second harmonic (532nm) or the third harmonic (355 nm) of an Nd:YVO₄ laser (fundamental waveof 1064 nm) can be used. In this case, the energy density ofapproximately 0.01 to 100 MW/cm² (preferably, 0.1 to 10 MW/cm²) isrequired for the laser. The scanning rate is set at approximately 10 to2000 cm/sec to irradiate the semiconductor film.

Note that a laser using, as a medium, single crystalline YAG, YVO₄,forsterite (Mg₂SiO₄), YAlO₃, or GdVO₄, or polycrystalline (ceramic) YAG,Y₂O₃, YVO₄, YAlO₃, or GdVO₄ doped with one or more of Nd, Yb, Cr, Ti,Ho, Er, Tm, and Ta as a dopant; an Ar ion laser; and a Ti:sapphire laserare capable of continuous oscillation. Further, pulse oscillationthereof can be performed at a repetition rate of 10 MHz or more bycarrying out Q switch operation or mode locking. When a laser beam isemitted at a repetition rate of 10 MHz or more, a semiconductor film isirradiated with a next pulse after being melted by the laser beam andbefore being solidified. Therefore, unlike a case of using a pulsedlaser with a low repetition rate, a solid-liquid interface can becontinuously moved in the semiconductor film; therefore, crystal grainswhich continuously grow in a scanning direction can be obtained.

When ceramic (polycrystal) is used as a medium, the medium can be formedto have a desired shape for a short time and at low cost. When a singlecrystalline is used, a columnar medium with several mm in diameter andseveral tens of mm in length is used. When the ceramic is used, a mediumlarger than the case of using the single crystalline can be formed.

A concentration of a dopant such as Nd or Yb in a medium, which directlycontributes to light emission, cannot be changed largely in either caseof the single crystalline or the polycrystal; therefore, there is somelimitation on improvement in output of a laser by increasing theconcentration of the dopant. However, in the case of ceramic, the sizeof a medium can be significantly increased as compared with the case ofthe single crystalline; therefore, drastic improvement in output of alaser can be expected.

Further, in the case of ceramic, a medium with a parallelepiped shape ora rectangular parallelepiped shape can be easily formed. When a mediumhaving such a shape is used and oscillated light is made travel in azigzag manner inside the medium, a path of the oscillated light can bemade long. Therefore, amplification is increased and a laser beam can beoscillated at high output. Furthermore, since a cross section of a laserbeam emitted from the medium having such a shape has a quadrangularshape, it has an advantage over a circular beam in being shaped into alinear beam. By shaping a laser beam emitted in the aforementionedmanner by using an optical system, a linear beam having a length of 1 mmor less on a lateral side and a length of several mm to several m on alongitudinal side can be easily obtained. In addition, when a medium isuniformly irradiated with excited light, energy distribution of a linearbeam becomes uniform in a longitudinal direction.

A semiconductor film is irradiated with this linear beam, so that thewhole surface of the semiconductor film can be annealed more uniformly.When uniform annealing is required from one end to the other end of thelinear beam, ingenuity such as arrangement in which slits are providedin ends of the linear beam to shield light at a portion where energy isattenuated is required.

When a semiconductor film is annealed using the thus obtained linearbeam having uniform intensity and an electronic appliance ismanufactured by using this semiconductor film, characteristics of theelectronic appliance are good and uniform.

As the method for crystallizing the amorphous semiconductor film byheating with an element which promotes crystallization of thesemiconductor film, a technique described in Japanese Published PatentApplication No. H8-78329 can be used. In the technique in the patentapplication publication, an amorphous semiconductor film (also referredto as an amorphous silicon film) is doped with a metal element whichpromotes crystallization of the semiconductor film, and then heattreatment is performed so that the amorphous semiconductor film iscrystallized with the doped region as a nucleus.

Alternatively, an amorphous semiconductor film can be crystallized byperforming irradiation with strong light instead of heat treatment. Inthis case, one of or a combination of infrared light, visible light, andultraviolet light can be used. Typically, light emitted from a halogenlamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a highpressure sodium lamp, or a high pressure mercury lamp is used. A lamplight source is lighted for 1 to 60 seconds, preferably 30 to 60seconds, and such lighting is repeated 1 to 10 times, preferably 2 to 6times. The light emission intensity of the lamp light source isarbitrary, but the semiconductor film is required to be instantaneouslyheated up to approximately 600 to 1000° C. Note that if necessary, heattreatment may be performed in order to discharge hydrogen contained inthe amorphous semiconductor film having an amorphous structure beforethe irradiation with the strong light. Alternatively, crystallizationmay be performed by both heat treatment and irradiation with stronglight.

After the heat treatment, in order to increase the degree ofcrystallinity of the crystalline semiconductor film (rate of areaoccupied by crystalline components against the whole volume of the film)and to correct defects which remain in crystalline grains, thecrystalline semiconductor film may be irradiated with the laser light inthe atmospheric air or an oxygen atmosphere. The laser light may beselected from the aforementioned laser light.

The doped elements are required to be removed from the crystallinesemiconductor film, and the method is described below. First, a surfaceof the crystalline semiconductor film is treated with a solutioncontaining ozone (typically, ozone water), so that a barrier layerformed of an oxide film (called chemical oxide) is formed on the surfaceof the crystalline semiconductor film to have a thickness of 1 to 10 nm.The barrier layer functions as an etching stopper when only a getteringlayer is selectively removed in a subsequent step.

Then, a gettering layer containing a rare gas element is formed as agettering site over the barrier layer. Here, a semiconductor filmcontaining a rare gas element is formed as the gettering layer by a CVDmethod or a sputtering method. When the gettering layer is formed, thesputtering conditions are controlled as appropriate so that a rare gaselement is added to the gettering layer. The rare gas element may be oneor more of helium (He), neon (Ne), argon (Ar), krypton (Kr), or xenon(Xe).

Note that when the gettering layer is formed by using a source gascontaining phosphorus which is an impurity element or by using a targetcontaining phosphorus, gettering can be performed by utilizing thecoulomb force of phosphorus in addition to the gettering using the raregas element. In gettering, a metal element (such as nickel) tends tomove to a region having a high concentration of oxygen; therefore, theconcentration of oxygen contained in the gettering layer is preferablyset at, for example, 5×10¹⁸/cm⁻³ or higher.

Next, the crystalline semiconductor film, the barrier layer, and thegettering layer are subjected to thermal treatment (such as heattreatment or irradiation with strong light), and thereby the metalelement (such as nickel) is gettered, so that the metal element in thecrystalline semiconductor film is lowered in concentration or removed.

Next, a known etching method is performed using the barrier layer as anetching stopper so that only the gettering layer is selectively removed.After that, the barrier layer formed of an oxide film is removed, forexample, using an etchant containing hydrofluoric acid.

Here, impurity ions may be added in consideration of thresholdcharacteristics of a TFT to be manufactured.

Next, a photo resist film (not shown) is applied over the crystallinesemiconductor film, and is exposed to light and developed. Therefore, aresist pattern is formed over the crystalline semiconductor film. Next,the crystalline semiconductor film is etched using the resist pattern asa mask. Therefore, a crystalline semiconductor film 803 to be includedin a thin film transistor and a crystalline semiconductor film 803 a tobe a common electrode are formed over the base film 802.

Next, after surfaces of the crystalline semiconductor films 803 and 803a are cleaned with an etchant containing hydrofluoric acid, a gateinsulating film 804 is formed to have a thickness of 10 to 200 nm overthe crystalline semiconductor film 803. The gate insulating film 804 isformed of an insulating film containing silicon as a main component,such as a silicon oxide film, a silicon nitride film, a siliconoxynitride film, or a silicon nitride oxide film. Further, the gateinsulating film may have a single layer or a stacked-layer film. Notethat the gate insulating film 804 is also formed over the crystallinesemiconductor film 803 a and the base film 802.

Next, as shown in FIG. 26C, after the gate insulating film 804 iscleaned, a first conductive film and a second conductive film are formedin this order over the gate insulating film 804. For example, the firstconductive film is a tungsten film and the second conductive film is atantalum nitride film.

Next, a photo resist film (not shown) is applied over the secondconductive film, and is exposed to light and developed. Therefore, aresist pattern is formed over the second conductive film. Next, by usingthe resist pattern as a mask, the first conductive film and the secondconductive film are etched under a first condition, and further, thesecond conductive film is etched under a second condition. Thus, firstgate electrodes 805 a and 805 b and second gate electrodes 806 a and 806b are formed over the crystalline semiconductor film 803. The first gateelectrodes 805 a and 805 b are separated from each other. The secondgate electrode 806 a is provided over the first gate electrode 805 a,and the second gate electrode 806 b is provided over the first gateelectrode 806 b. Inclined angles of side surfaces of each of the firstgate electrodes 805 a and 805 b are more moderate than inclined anglesof side surfaces of each of the second gate electrodes 806 a and 806 b.

By the etching treatment, a first wiring 807 and a second wiring 808provided over the first wiring 807 are formed near the crystallinesemiconductor film 803 a. Here, each of the aforementioned gateelectrodes and wirings is preferably led so as to have a round cornerwhen seen from a direction perpendicular to the substrate 801. By makingthe corners round, dust or the like can be prevented from remaining atthe corners of the wiring; therefore, the number of defects generateddue to dust can be reduced and yield can be improved. Thereafter, thephoto resist film is removed.

Next, as shown in FIG. 26D, a first conductivity type (for example,n-type) impurity element (for example, phosphorus) is injected into thecrystalline semiconductor film 803 by using the first gate electrodes805 a and 805 b and the second gate electrodes 806 a and 806 b as masks.Therefore, first impurity regions 810 a, 810 b, and 810 c are formed inthe crystalline semiconductor film 803. The first impurity region 810 ais provided in a region to be a source of the thin film transistor. Thefirst impurity region 810 c is provided in a region to be a drain of thethin film transistor. The impurity region 810 b is provided between thefirst gate electrodes 805 a and 805 b.

Note that in this treatment, the first conductivity type impurityelement is also injected into the crystalline semiconductor film 803 ato be a common electrode to lower resistance.

Next, as shown in FIG. 26E, a photo resist film is applied over thewhole surface including over the first gate electrodes 805 a and 805 band the second gate electrodes 806 a and 806 b, and is exposed to lightand developed. Therefore, each of top surfaces of the first gateelectrode 805 a and the second gate electrode 806 a and theirsurroundings are covered with a resist pattern 812 a, and each of topsurfaces of the first gate electrode 805 b and the second gate electrode806 b and their surroundings are covered with a resist pattern 812 b.Next, by using the resist patterns 812 a and 812 b as masks, a firstconductivity type impurity element 811 (for example, phosphorus) isinjected into the crystalline semiconductor film 803. Therefore, thefirst conductivity type impurity element 811 is further injected into apart of each of the first impurity regions 810 a, 810 b, and 810 c, sothat second impurity regions 813 a, 813 b, and 813 c are formed.

Further, the first conductivity type impurity element is furtherinjected into the crystalline semiconductor film 803 a to be the commonelectrode to lower resistance. Note that the other parts of the firstimpurity regions 810 a, 810 b, and 810 c remain as third impurityregions 814 a, 814 b, 814 c, and 814 d.

Thereafter, as shown in FIG. 27A, the resist patterns 812 a and 812 bare removed. Next, an insulating film (not shown) covering almost allsurface is formed. The insulating film is, for example, a silicon oxidefilm formed by a plasma CVD method.

Next, heat treatment is performed on the crystalline semiconductor films803 and 803 a to activate the impurity elements doped therewith. Theheat treatment is performed by a rapid thermal annealing method (RTAmethod) using a lamp light source, irradiation of a YAG laser or anexcimer laser from the back surface, or heat treatment using a furnace,or by a combination of a plurality of these methods.

By the aforementioned treatment, the impurity elements are activated,and simultaneously the element (for example, a metal element such asnickel), which is used as a catalyst for crystallizing the crystallinesemiconductor film 803, is gettered in the second impurity regions 813 ato 813 c including a high concentration impurity (such as phosphorus),and a nickel concentration mainly in a region to be a channel formingregion of the crystalline semiconductor film 803 is reduced. As aresult, crystallinity of the channel forming region is improved.Accordingly, an off-current value of a TFT is reduced and high electronfield-effect mobility can be obtained. Therefore, a TFT having favorablecharacteristics can be obtained.

Next, an insulating film 815 is formed over the whole surface includingabove the crystalline semiconductor films 803 and 803 a. The insulatingfilm 815 is, for example, a silicon nitride film formed by a plasma CVDmethod. Next, a planarizing film to be an interlayer insulating film 816is formed over the insulating film 815. As the interlayer insulatingfilm 816, a light-transmitting inorganic material (silicon oxide,silicon nitride, silicon nitride containing oxygen, or the like); aphotosensitive or non-photosensitive organic material (polyimide,acrylic, polyamide, polyimide amide, a resist, or benzocyclobutene); astacked-layer structure thereof; or the like is used. Alternatively, asanother light-transmitting film used for the planarizing film, aninsulating film formed of a SiO_(x) film containing an alkyl groupobtained by a coating method, for example, an insulating film usingsilica glass, alkyl siloxane polymers, alkylsilsesquioxane polymers,hydrogen silsesquioxane polymers, hydrogen alkylsilsesquioxane polymers,or the like can be used. As an example of siloxane-based polymers, thereare coating insulating film materials such as PSB-K1 and PSB-K31(product of Toray industries, Inc.) and ZRS-5PH (product of Catalysts &Chemicals Industries Co., Ltd.). The interlayer insulating film may be asingle-layer film or a multi-layer film.

Next, a photo resist film (not shown) is applied over the interlayerinsulating film 816, and is exposed to light and developed. Therefore, aresist pattern is formed over the interlayer insulating film 816. Next,the interlayer insulating film 816, the insulating film 815, and thegate insulating film 804 are etched using the resist pattern as a mask.Therefore, contact holes 817 a, 817 b, 817 c, and 817 d are formed inthe interlayer insulating film 816, the insulating film 815, and thegate insulating film 804. The contact hole 817 a is provided over thesecond impurity region 813 a, which is the source of the transistor. Thecontact hole 817 b is provided over the second impurity region 813 c,which is the drain of the transistor. The contact hole 817 c is providedover the second wiring 808. The contact hole 817 d is provided over thecrystalline semiconductor film 803 a, which is the common electrode.Thereafter, the resist pattern is removed.

Next, as shown in FIG. 27B, a first conductive film 818 is formed ineach of the contact holes 817 a to 817 d and over the interlayerinsulating film 816. The first conductive film 818 is alight-transmitting conductive film, such as an ITO film, a film ofindium tin oxide containing a Si element, or a film of IZO (indium zincoxide) formed by using a target in which zinc oxide (ZnO) of 2 to 20 wt% is mixed with indium oxide. Next, a second conductive film 819 isformed over the first conductive film 818. The second conductive film819 is, for example, a metal film.

Next, a photo resist film 820 is applied over the conductive film 819.Next, a reticle 840 is provided above the photo resist film 820. Thereticle 840 has a structure where semi-transmitting film patterns 842 a,842 b, 842 c, and 842 d are formed over a glass substrate and lightshielding patterns 841 a, 841 b, and 841 c are formed over a part of thesemi-transmitting film patterns 842 a to 842 d. The semi-transmittingfilm pattern 842 a and the light shielding pattern 841 a are providedabove the contact hole 817 a. The semi-transmitting film pattern 842 band the light shielding pattern 841 b are provided above the contacthole 817 b. The semi-transmitting film pattern 842 c and the lightshielding pattern 841 c are provided above the contact holes 817 c and817 d. The semi-transmitting film pattern 842 d is provided above thecrystalline semiconductor film 803 a.

Next, the photo resist film 820 is exposed to light using the reticle840 as a mask. Therefore, the photo resist film 820 is exposed to lightexcept for a portion below the light shielding patterns 841 a to 841 cand a lower layer of a portion below the semi-transmitting film patterns842 a to 842 d. Note that portions which are not exposed to light aredenoted by reference numerals 821 a, 821 b, 821 c, and 821 d.

Next, as shown in FIG. 27C, the photo resist film 820 is developed.Therefore, portions exposed to light in the photo resist film 820 areremoved, and resist patterns 822 a, 822 b, 822 c, and 822 d are formed.The resist pattern 822 a is provided above the contact hole 817 a. Theresist pattern 822 b is provided above and around the contact hole 817b. The resist pattern 822 c is provided above and between the contactholes 817 c and 817 d. The resist pattern 822 d is provided above thecrystalline semiconductor film 803 a to be the common electrode. Notethat portions of the resist pattern 822 b, except for a portion abovethe contact hole 817 b, and the resist pattern 822 d are thinner thanother resist patterns.

Next, as shown in FIG. 27D, the first conductive film 818 and the secondconductive film 819 are etched using the resist patterns 822 a to 822 das masks. Thus, the first conductive film 818 and the second conductivefilm 819 in regions which are not covered with the resist patterns 822 ato 822 d are removed.

Further, since the resist patterns 822 a to 822 d are also graduallyetched, in the etching treatment, a thin portion (specifically, theportions of the resist pattern 822 b, except for a portion above thecontact hole 817 b, and the resist pattern 817 d) of the resist patternis removed. Therefore, in each of regions below the portion of theresist pattern 822 b except for a portion above the contact hole 817 b,and the resist pattern 817 d, the second conductive film 819 is removedand only the first conductive film 818 remains. Thereafter, the resistpatterns 822 a to 822 c are removed.

As described above, with one resist pattern and one etching treatment,source wirings 823 a and 824 a, drain wiring 823 b and 824 b, connectionwirings 823 c and 824 c, and a pixel electrode 823 d are formed. Thesource wirings 823 a and 824 a and the drain wiring 823 b and 824 b forma thin film transistor 825 along with the crystalline semiconductor film803, impurity regions formed in the crystalline semiconductor film 803,the gate insulating film 804, the first gate electrodes 805 a and 805 b,and the second gate electrodes 806 a and 806 b. The connection wirings823 c and 824 c connect the second wiring 808 and the crystallinesemiconductor film 803 a.

Thereafter, a first alignment film 826 is formed. Thus, an active matrixsubstrate is formed. Note that with the treatments shown in FIGS. 26A to27D, thin film transistors 827 and 829 (shown in FIG. 28B) are formed ina gate signal line driver circuit region 854 of a liquid crystal displaydevice shown in FIGS. 28A and 28B. Further, with the treatments shown inFIGS. 27B to 27D, a first terminal electrode 838 a and a second terminalelectrode 838 b (shown in FIG. 28B) which connect the active matrixsubstrate and the outside are formed.

Thereafter, as shown in a plan view of FIG. 28A and a cross-sectionalview along a line K-L of FIG. 28B, an organic resin film such as anacrylic resin film is formed over the active matrix substrate, andpatterning is performed on the organic resin film. Thus, a columnarspacer 833 is formed over the active matrix substrate. Next, after asealing material 834 is formed in a sealing region 853, a liquid crystalis dropped on the active matrix substrate. Before the liquid crystal isdropped, a protective film may be formed over the sealing material toprevent the sealing material and the liquid crystal from reacting witheach other.

Thereafter, an opposite substrate 830 provided with a color filter 832and a second alignment film 831 is provided opposed to the active matrixsubstrate, and these two substrates are attached by the sealing material834. In this case, the active matrix substrate and the oppositesubstrate 830 are attached by the spacer 833 to have a uniformed space.Next, the space between the substrates is completely sealed. Thus, theliquid crystal is sealed between the active matrix substrate and theopposite substrate.

Next, if required, one or both the active matrix substrate and theopposite substrate are cut into a desired shape. Further, polarizingplates 835 a and 835 b are provided. Next, a flexible printed circuit(hereinafter referred to as an FPC) 837 is connected to the secondterminal electrode 838 b provided in an external terminal connectionregion 852, through an anisotropy conductive film 836.

A structure of the liquid crystal display module formed in this manneris described. A pixel region 856 is provided at the center of the activematrix substrate. A plurality of pixels are formed in the pixel region856. In FIG. 28A, the gate signal line driver circuit regions 854 fordriving a gate signal line are provided above and below the pixel region856. A source signal line driver circuit region 857 for driving a sourcesignal line is provided in a region between the pixel region 856 and theFPC 837. The gate signal line driver circuit region 854 may be providedeither above and below the pixel region 856, which may be selected by adesigner as appropriate in accordance with substrate size in the liquidcrystal display module, or the like. Note that when operationreliability, efficiency of driving, and the like of the circuits areconsidered, the gate signal line driver circuit regions 854 arepreferably provided symmetrically with the pixel region 856therebetween. Signals to each driver circuit are inputted from the FPC837.

Embodiment 2

A liquid crystal display module according to Embodiment 2 of the presentinvention is described with reference to FIGS. 29A to 30B. In eachdrawing, a structure of a pixel portion 930 is similar to that of thepixel region 856 shown in Embodiment 1, and a plurality of pixels areformed over the substrate 100.

FIG. 29A is a schematic plan view of a liquid crystal display module.FIG. 29B is a diagram illustrating a circuit structure of a sourcedriver 910. As an example of FIGS. 29A and 29B, both a gate driver 920and the source driver 910 are formed over the substrate 100 same as thepixel portion 930 as shown in FIG. 29A. The source driver 910 includes aplurality of thin film transistors 912 for selecting the source signalline to which an inputted video signal is transmitted; and a shiftregister 911 for controlling the plurality of thin film transistors 912.

FIG. 30A is a schematic plan view of a liquid crystal display module.FIG. 30B is a diagram illustrating a circuit structure of a sourcedriver. As an example of FIGS. 30A and 30B, the source driver includes athin film transistor group 940 formed over the substrate 100; and an IC950 formed separately from the substrate 100. The IC 950 and the thinfilm transistor group 940 are electrically connected by an FPC 960, forexample.

The IC 950 is formed using a single crystalline silicon substrate, forexample. The IC 950 controls the thin film transistor group 940 andinputs a video signal to the thin film transistor group 940. The thinfilm transistor group 940 selects the source signal line to which aninputted video signal is transmitted, based on a control signal from theIC.

According to Embodiment 2, manufacturing cost of a liquid crystaldisplay module can be reduced.

Embodiment 3

An electric appliance according to Embodiment 3 of the present inventionis described with reference to FIGS. 31A to 31H. An electric applianceincludes a light emitting device of the present invention and isprovided with a module such as examples shown in the aforementionedembodiments.

The electronic appliances include cameras such as a video camera and adigital camera, a goggle-type display (head mounted display), anavigation system, an audio reproducing device (such as a car audiocomponent stereo), a computer, a game machine, a portable informationterminal (such as a mobile computer, a mobile phone, a mobile gamemachine, and an electronic book), an image reproducing device providedwith a recording medium (specifically, a device for reproducing arecording medium such as a digital versatile disc (DVD) and having adisplay for displaying the reproduced image) and the like. FIGS. 31A to31H show specific examples of these electric appliances.

FIG. 31A shows a monitor of a television receiving device or a personalcomputer, which includes a housing 2001, a supporting base 2002, adisplay portion 2003, a speaker portion 2004, a video input terminal2005, and the like. As the display portion 2003, the liquid crystaldisplay device shown in any of Embodiment Modes 1 to 20 is used. Sincethe monitor of the television receiving device or the personal computerincludes the liquid crystal display device, manufacturing cost thereofcan be reduced.

FIG. 31B shows a digital camera. An image receiving portion 2103 isprovided in the front side of a main body 2101. A shutter 2106 isprovided at the upper portion of the main body 2101. A display portion2102, operation keys 2104, and an external connection port 2105 areprovided at the backside of the main body 2101. As the display portion2103, the liquid crystal display device shown in any of Embodiment Modes1 to 20 is used. Since the digital camera includes the liquid crystaldisplay device, manufacturing cost thereof can be reduced.

FIG. 31C shows a notebook computer. A main body 2201 is provided with akeyboard 2204, an external connection port 2205, and a pointing device2206. A housing 2202 including a display portion 2203 is attached to themain body 2201. As the display portion 2203, the liquid crystal displaydevice shown in any of Embodiment Modes 1 to 20 is used. Since thenotebook computer includes the liquid crystal display device,manufacturing cost thereof can be reduced.

FIG. 31D shows a mobile computer, which includes a main body 2301, adisplay portion 2302, a switch 2303, operation keys 2304, an infraredport 2305, and the like. An active matrix display device is provided forthe display portion 2302. As the display portion 2303, the liquidcrystal display device shown in any of Embodiment Modes 1 to 20 is used.Since the mobile computer includes the liquid crystal display device,manufacturing cost thereof can be reduced.

FIG. 31E shows an image reproducing device. A main body 2401 is providedwith a display portion B 2404, a recording medium reading portion 2405,and an operation key 2406. A housing 2402 including a speaker portion2407 and a display portion A 2403 is attached to the main body 2401. Aseach of the display portion A 2403 and the display portion B 2404, theliquid crystal display device shown in any of Embodiment Modes 1 to 20is used. Since the image reproducing device includes the liquid crystaldisplay device, manufacturing cost thereof can be reduced.

FIG. 31F shows an electronic book. A main body 2501 is provided with anoperation key 2503. A plurality of display portions 2502 are attached tothe main body 2501. As the display portions 2502, the liquid crystaldisplay device shown in any of Embodiment Modes 1 to 20 is used. Sincethe electronic book includes the liquid crystal display device,manufacturing cost thereof can be reduced.

FIG. 31G shows a video camera. A main body 2601 is provided with anexternal connection port 2604, a remote control receiving portion 2605,an image receiving portion 2606, a battery 2607, an audio input portion2608, operation keys 2609, and an eyepiece portion 2610. A housing 2603including a display portion 2602 is attached to the main body 2601. Asthe display portions 2602, the liquid crystal display device shown inany of Embodiment Modes 1 to 20 is used. Since the video camera includesthe liquid crystal display device, manufacturing cost thereof can bereduced.

FIG. 31H shows a mobile phone, which includes a main body 2701, ahousing 2702, a display portion 2703, an audio input portion 2704, anaudio output portion 2705, an operation key 2706, an external connectionport 2707, an antenna 2708, and the like. As the display portions 2703,the liquid crystal display device shown in any of Embodiment Modes 1 to20 is used. Since the mobile phone includes the liquid crystal displaydevice, manufacturing cost thereof can be reduced.

As described above, the application range of the present invention is sowide that the present invention can be applied to electronic appliancesof various fields.

This application is based on Japanese Patent Application serial No.2006-105618 filed in Japan Patent Office on Apr. 6, 2006, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A liquid crystal display device comprising: afirst substrate; a first gate electrode over the first substrate; a gateinsulating layer over the first gate electrode; a semiconductor layercomprising a channel formation region over the first gate electrode withthe gate insulating layer interposed therebetween; a common electrodeover the gate insulating layer; an insulating layer over thesemiconductor layer and the common electrode; a pixel electrode over theinsulating layer; a liquid crystal layer over the pixel electrode; and asecond substrate over the liquid crystal layer, wherein each of thesemiconductor layer and the common electrode comprises indium and zinc,wherein the pixel electrode overlaps with the common electrode with theinsulating layer interposed therebetween to form a capacitor, whereinthe pixel electrode is electrically connected to the semiconductorlayer, wherein the common electrode comprises the same material as thesemiconductor layer, and wherein the semiconductor layer and the commonelectrode have substantially the same thickness.
 2. The liquid crystaldisplay device according to claim 1, wherein the insulating layercomprises nitrogen.
 3. The liquid crystal display device according toclaim 1, wherein the liquid crystal layer is configured to be driven byan electric field generated between the pixel electrode and the commonelectrode.
 4. The liquid crystal display device according to claim 1,wherein each of the semiconductor layer and the common electrode furthercomprises gallium.
 5. The liquid crystal display device according toclaim 1, wherein each of the semiconductor layer and the commonelectrode comprises a-InGaZnO.
 6. The liquid crystal display deviceaccording to claim 1, wherein the gate insulating layer comprisesnitrogen.
 7. The liquid crystal display device according to claim 1,wherein the insulating layer comprises an opening overlapping with thecommon electrode.
 8. The liquid crystal display device according toclaim 1, further comprising a second gate electrode over the firstsubstrate, wherein the semiconductor layer is provided over the secondgate electrode with the gate insulating layer interposed therebetween.9. The liquid crystal display device according to claim 1, furthercomprising a wiring over the first substrate, wherein the gateinsulating layer is over the wiring, and wherein the wiring iselectrically connected to the common electrode.
 10. The liquid crystaldisplay device according to claim 1, wherein the common electrodecomprises an impurity to enhance a conductivity of the common electrode.11. The liquid crystal display device according to claim 10, wherein theimpurity is at least one selected from the group consisting ofphosphorus, boron, gallium, and arsenic.
 12. The liquid crystal displaydevice according to claim 1, wherein the semiconductor layer and thecommon electrode are formed by a process comprising the steps of:forming a semiconductor film over the gate insulating layer; and etchingthe semiconductor film to form the semiconductor layer and the commonelectrode.
 13. A liquid crystal display device comprising: a substrate;a first gate electrode over the substrate; a gate insulating layer overthe first gate electrode; a semiconductor layer over the first gateelectrode with the gate insulating layer interposed therebetween; afirst electrode over the gate insulating layer; an insulating layer overthe semiconductor layer and the first electrode; a pixel electrode overthe insulating layer; and a liquid crystal layer over the pixelelectrode, wherein each of the semiconductor layer and the firstelectrode comprises indium and zinc, wherein the pixel electrodeoverlaps with the first electrode with the insulating layer interposedtherebetween to form a capacitor, wherein the pixel electrode iselectrically connected to the semiconductor layer, wherein the firstelectrode comprises the same material as the semiconductor layer, andwherein the semiconductor layer and the first electrode havesubstantially the same thickness.
 14. The liquid crystal display deviceaccording to claim 13, wherein the insulating layer comprises nitrogen.15. The liquid crystal display device according to claim 13, wherein theliquid crystal layer is configured to be driven by an electric fieldgenerated between the pixel electrode and the first electrode.
 16. Theliquid crystal display device according to claim 13, wherein each of thesemiconductor layer and the first electrode further comprises gallium.17. The liquid crystal display device according to claim 13, whereineach of the semiconductor layer and the first electrode comprisesa-InGaZnO.
 18. The liquid crystal display device according to claim 13,wherein the gate insulating layer comprises nitrogen.
 19. The liquidcrystal display device according to claim 13, wherein the insulatinglayer comprises an opening overlapping with the first electrode.
 20. Theliquid crystal display device according to claim 13, further comprisinga second gate electrode over the substrate, wherein the semiconductorlayer is provided over the second gate electrode with the gateinsulating layer interposed therebetween.
 21. The liquid crystal displaydevice according to claim 13, further comprising a wiring over thesubstrate, wherein the gate insulating layer is over the wiring, andwherein the wiring is electrically connected to the first electrode. 22.The liquid crystal display device according to claim 13, wherein thefirst electrode comprises an impurity to enhance a conductivity of thefirst electrode.
 23. The liquid crystal display device according toclaim 22, wherein the impurity is at least one selected from the groupconsisting of phosphorus, boron, gallium, and arsenic.
 24. The liquidcrystal display device according to claim 13, wherein the semiconductorlayer and the first electrode are formed by a process comprising thesteps of: forming a semiconductor film over the gate insulating layer;and etching the semiconductor film to form the semiconductor layer andthe first electrode.
 25. A liquid crystal display device comprising: asubstrate; a first gate electrode over the substrate; a gate insulatinglayer over the first gate electrode; a semiconductor layer over thefirst gate electrode with the gate insulating layer interposedtherebetween; a first electrode on and in contact with the gateinsulating layer; an insulating layer over the semiconductor layer andthe first electrode; a pixel electrode over the insulating layer; and aliquid crystal layer over the pixel electrode, wherein each of thesemiconductor layer and the first electrode comprises indium and zinc,wherein the pixel electrode overlaps with the first electrode with theinsulating layer interposed therebetween to form a capacitor, whereinthe pixel electrode is electrically connected to the semiconductorlayer, wherein the first electrode comprises the same material as thesemiconductor layer, and wherein the semiconductor layer and the firstelectrode have substantially the same thickness.
 26. The liquid crystaldisplay device according to claim 25, wherein the insulating layercomprises nitrogen.
 27. The liquid crystal display device according toclaim 25, wherein the liquid crystal layer is configured to be driven byan electric field generated between the pixel electrode and the firstelectrode.
 28. The liquid crystal display device according to claim 25,wherein each of the semiconductor layer and the first electrode furthercomprises gallium.
 29. The liquid crystal display device according toclaim 25, wherein each of the semiconductor layer and the firstelectrode comprises a-InGaZnO.
 30. The liquid crystal display deviceaccording to claim 25, wherein the gate insulating layer comprisesnitrogen.
 31. The liquid crystal display device according to claim 25,wherein the insulating layer comprises an opening overlapping with thefirst electrode.
 32. The liquid crystal display device according toclaim 25, further comprising a second gate electrode over the substrate,wherein the semiconductor layer is provided over the second gateelectrode with the gate insulating layer interposed therebetween. 33.The liquid crystal display device according to claim 25, furthercomprising a wiring over the substrate, wherein the gate insulatinglayer is over the wiring, and wherein the wiring is electricallyconnected to the first electrode.
 34. The liquid crystal display deviceaccording to claim 25, wherein the first electrode comprises an impurityto enhance a conductivity of the first electrode.
 35. The liquid crystaldisplay device according to claim 34, wherein the impurity is at leastone selected from the group consisting of phosphorus, boron, gallium,and arsenic.
 36. The liquid crystal display device according to claim25, wherein the semiconductor layer and the first electrode are formedby a process comprising the steps of: forming a semiconductor film overthe gate insulating layer; and etching the semiconductor film to formthe semiconductor layer and the first electrode.
 37. A liquid crystaldisplay device comprising: a substrate; a first gate electrode over thesubstrate; a gate insulating layer over the first gate electrode; asemiconductor layer over the first gate electrode with the gateinsulating layer interposed therebetween; a first electrode over thegate insulating layer; an insulating layer over the semiconductor layerand the first electrode; a pixel electrode over the insulating layer;and a liquid crystal layer over the pixel electrode; wherein each of thesemiconductor layer and the first electrode comprises indium and zinc,wherein the pixel electrode overlaps with the first electrode with theinsulating layer interposed therebetween to form a capacitor, whereinthe first electrode is in contact with the insulating layer, wherein thefirst electrode comprises the same material as the semiconductor layer,and wherein the semiconductor layer and the first electrode havesubstantially the same thickness.
 38. The liquid crystal display deviceaccording to claim 37, wherein the insulating layer comprises nitrogen.39. The liquid crystal display device according to claim 37, wherein theliquid crystal layer is configured to be driven by an electric fieldgenerated between the pixel electrode and the first electrode.
 40. Theliquid crystal display device according to claim 37, wherein each of thesemiconductor layer and the first electrode further comprises gallium.41. The liquid crystal display device according to claim 37, whereineach of the semiconductor layer and the first electrode comprisesa-InGaZnO.
 42. The liquid crystal display device according to claim 37,wherein the gate insulating layer comprises nitrogen.
 43. The liquidcrystal display device according to claim 37, wherein the insulatinglayer comprises an opening overlapping with the first electrode.
 44. Theliquid crystal display device according to claim 37, further comprisinga second gate electrode over the substrate, wherein the semiconductorlayer is provided over the second gate electrode with the gateinsulating layer interposed therebetween.
 45. The liquid crystal displaydevice according to claim 37, further comprising a wiring over thesubstrate, wherein the gate insulating layer is over the wiring, andwherein the wiring is electrically connected to the first electrode. 46.The liquid crystal display device according to claim 37, wherein thefirst electrode comprises an impurity to enhance a conductivity of thefirst electrode.
 47. The liquid crystal display device according toclaim 46, wherein the impurity is at least one selected from the groupconsisting of phosphorus, boron, gallium, and arsenic.
 48. The liquidcrystal display device according to claim 37, wherein the semiconductorlayer and the first electrode are formed by a process comprising thesteps of: forming a semiconductor film over the gate insulating layer;and etching the semiconductor film to form the semiconductor layer andthe first electrode.